Volumetric Power Input Research Articles

Scale-up of CHO cell cultures: from 96-well-microtiter plates to stirred tank reactors across three orders of magnitude.

For process development in mammalian cell cultivations, scale-up approaches are essential. A lot of studies concern the scale transfer between different-sized stirred tank reactors. However, process development usually starts in even smaller cultivation vessels like microtiter plates or shake flasks. A scale-up from those small shaken devices to a stirred tank reactor is barely stated in literature for mammalian cells. Thus, this study aims to address data-driven scale-up for CHODP12 cells. The oxygen transfer rate is used as a database. The cultivation conditions in microtiter plates and shake flasks are comparable when choosing the maximum oxygen transfer capacity as a scale-up parameter. The minimum cultivation volume was reduced to 400µL in round and square 96-deep-well microtiter plates. Using a scale-up based on the maximum oxygen transfer capacity to a stirred tank reactor led to conditions with excessive hydromechanical stress. However, cultivation conditions could be reproduced in a stirred tank reactor by utilizing the volumetric power input as a scale-up parameter. Key metabolites behaved the same in all three scales and the final antibody titer was equal. This study presents a successful replication of cultivation results for mammalian cells in microtiter plates, shake flasks and stirred tank reactors. The working volumes ranged from 0.4 to 50 and 600mL. It offers the opportunity to adapt the method to other, more sensitive mammalian cells and to perform cost- and time-effective experiments in high-throughput.

Exploration of the Out‐of‐Phase Phenomenon in Shake Flasks by CFD Calculations of Volumetric Power Input, kLa Value and Shear Rate at Elevated Viscosity

ABSTRACTCulture broth with secreted macromolecules and culture broth of filamentous fungi showing disperse growth exhibit elevated viscosity, usually with shear‐thinning flow behavior. High viscosity, however, poses a serious challenge in the production and research of these compounds and organisms. It commonly causes insufficient mixing and oxygen transfer in large‐ and small‐scale bioreactors. Computational Fluid dynamics (CFD) has been proven to be a valuable tool for the computation of important bioprocess parameters. The published literature for small‐scale shaken bioreactors, especially shake flasks, however, almost exclusively focuses on water‐like viscosity. In this paper, a previously published CFD model for 250 mL shake flasks was used to simulate experiments at high viscosities of up to 100 mPa·s. Compared to experimental data, the CFD model accurately predicted the liquid distribution and computed the volumetric power input with a deviation of less than 7% and the kLa value within a factor of two, compared to the kLa correlation from Henzler and Schedel. Furthermore, a novel approach to compute the shear rate was tested. Lastly, new insights into the out‐of‐phase phenomenon were gained. The presented data confirms the usefulness of the already established critical phase numbers of 0.91 and 1.26, while underlying the fundamentally smooth transition from in‐phase to out‐of‐phase operating conditions.

Novel sparging strategies to enhance dissolved carbon dioxide stripping in industrial scale stirred tank reactors

Aerated stirred tank reactors are widely used in bio-process engineering and pharmaceutical industries. To supply the organisms with oxygen and control the pH value, oxygen is transferred from air bubbles into the liquid phase, and, at the same time, carbon dioxide is stripped from the liquid phase with the same gas bubbles. The volumetric mass transfer coefficients for oxygen and carbon dioxide are, therefore, of crucial importance for the design and scale-up of aerated stirred tank reactors. In this experimental work, the volumetric mass transfer coefficients for oxygen and carbon dioxide are investigated simultaneously to study their mutual influence. The mass transfer performance for oxygen and carbon dioxide is conducted in stirred tank reactors on the 3 L laboratory scale, 30 L pilot scale, and 15,000 L production scale. First, the influence of dissolved carbon dioxide on the oxygen mass transfer performance is investigated in a 30 L pilot scale stirred tank reactor. The results show that the volumetric mass transfer coefficient of oxygen is not affected by the concentration of dissolved carbon dioxide, but the total mass flux of oxygen decreases with increasing carbon dioxide concentration due to the decreasing partial pressure difference. With rising gassing rate and volumetric power input, both mass transfer coefficients for oxygen and carbon dioxide show the same increasing trend. Although this trend can also be observed when scaling down to the 3 L laboratory scale reactor, a significantly different effect must be considered for the scale-up to the 15,000 L industrial scale reactor. The limited absorption capacity for carbon dioxide of the gas bubbles during the long residence time in the industrial scale reactor is noticeable here, which is why the specific interfacial area is of negligible importance. This effect is used to develop a method for independent control of oxygen and carbon dioxide mass transfer performance on an industrial scale and to increase the mass transfer performance for carbon dioxide by up to 25%.

CHO stable pool fed-batch process development of SARS-CoV-2 spike protein production: Impact of aeration conditions and feeding strategies.

Technology scale-up and transfer are a fundamental and critical part of process development in biomanufacturing. Important bioreactor hydrodynamic characteristics such as working volume, overhead gas flow rate, volumetric power input (P/V), impeller type, agitation regimen, sparging aeration strategy, sparger type, and kLa must be selected based on key performance indicators (KPI) to ensure a smooth and seamless process scale-up and transfer. Finding suitable operational setpoints and developing an efficient feeding regimen to ensure process efficacy and consistency are instrumental. In this investigation, process development of a cumate inducible Chinese hamster ovary (CHO) stable pool expressing trimeric SARS-CoV-2 spike protein in 1.8 L benchtop stirred-tank bioreactors is detailed. Various dissolved oxygen levels and aeration air caps were studied to determine their impact on cell growth and metabolism, culture longevity, and endpoint product titers. Once hydrodynamic conditions were tuned to an optimal zone, various feeding strategies were explored to increase culture performance. Dynamic feedings such as feeding based on current culture volume, viable cell density (VCD), oxygen uptake rate (OUR), and bio-capacitance signals were tested and compared to standard bolus addition. Increases in integral of viable cell concentration (IVCC) (1.25-fold) and protein yield (2.52-fold), as well as greater culture longevity (extension of 5 days) were observed in dynamic feeding strategies when compared to periodic bolus feeding. Our study emphasizes the benefits of designing feeding strategies around metabolically relevant signals such as OUR and bio-capacitance signals.

Design and scale up of a mixing process for a novel automotive coating

The study reported here was performed as part of a larger project aiming to develop a high performance automotive coating and the associated manufacturing process to enable large scale manufacture of the new product. We report from the process development aspect of the project which aimed at establishing the comparative blending performance of two types of impeller- one currently in use and an alternative- at different scales. Mixing time measurements compared on the basis of volumetric power input were comparable for the sawtooth impeller and pitched blade turbine over the turbulent and transitional regimes at formulation (T= 0.13 m, ∼2 l) and pilot scales (T= 0.30 m, ∼ 20 l). At the largest scale of ∼ 160 l, it took a lot longer to blend when using the sawtooth impeller. Measured mixing time results were in agreement with predicted values using the well-established correlation for both impellers in T= 0.30 m and also for the PBT at large scale, For the sawtooth impeller the correlation underpredicted at large scale unless a higher value for the constant in the mixing time correlation (about twice) was used. This deviation in the performance at large scale has highlighted the complexity of design and scale up using a sawtooth impeller.

Validation of computational fluid dynamics of shake flask experiments at moderate viscosity by liquid distributions and volumetric power inputs

Computational fluid dynamics (CFD) has recently become a pivotal tool in the design and scale-up of bioprocesses. While CFD has been extensively utilized for stirred tank reactors (STRs), there exists a relatively limited body of literature focusing on CFD applications for shake flasks, almost exclusively concentrated on fluids at waterlike viscosity. The importance of CFD model validation cannot be overstated. While techniques to elucidate the internal flow field are necessary for model validation in STRs, the liquid distribution, caused by the orbital shaking motion of shake flasks, can be exploited for model validation. An OpenFOAM CFD model for shake flasks has been established. Calculated liquid distributions were compared to suitable, previously published experimental data. Across a broad range of shaking conditions, at waterlike and moderate viscosity (16.7 mPa∙s), the CFD model's liquid distributions align excellently with the experimental data, in terms of overall shape and position of the liquid relative to the direction of the centrifugal force. Additionally, the CFD model was used to calculate the volumetric power input, based on the energy dissipation. Depending on the shaking conditions, the computed volumetric power inputs range from 0.1 to 7 kW/m3 and differed on average by 0.01 kW/m3 from measured literature data.

Scale-up analysis of geometrically dissimilar single-use bioreactors.

Cell culture scale-up is a challenging task due to the simultaneous change of multiple hydrodynamic process characteristics and their different dependencies on the bioreactor size as well as variation in the requirements of individual cell lines. Conventionally, the volumetric power input is the most common parameter to select the impeller speed for scale-up, however, it is well reported that this approach fails when there are huge differences in bioreactor scales. In this study, different scale-up criteria are evaluated. At first, different hydrodynamic characteristics are assessed using computational fluid dynamics data for four single-use bioreactors, the Mobius® CellReady 3 L, the Xcellerex™ XDR-10, the Xcellerex™ XDR-200, and the Xcellerex™ XDR-2000. On the basis of this numerical data, several potential scale-up criteria such as volumetric power input, impeller tip speed, mixing time, maximum hydrodynamic stress, and average strain rate in the impeller zone are evaluated. Out of all these criteria, the latter is found to be most appropriate, and the successful scale-up from 3to 10 L bioreactor and to 200 L bioreactor is confirmed with cell culture experiments using Chinese Hamster Ovary cell cultivation.

A modelling approach for volumetric power input in the microscale and its utilization for the scale-up of solid-liquid mixing systems

Many unit operations in bioprocessing engineering rely on adequate mixing. During process development, scale-up of unit operations is a critical, often laborious multistep task. Volumetric power input is used as one scale-up criteria for operations in stirred systems. While for stirred tank reactors the volumetric power input can be calculated from the Power Number Ne or extracted from literature, currently microtiter plates (MTPs) require experimental determination of power input for each process condition and geometry. We established data-driven models to predict the volumetric power input in shaken 24-, and 96-well MTPs without further experiments. The models were then applied to predict process conditions for the efficient solubilization of buffer components. Dissolution kinetics obtained in a continuous 10 L bench-scale system with baffles and a Rushton turbine were similar to those determined in 96-well MTPs. Combining the developed model with a geometrical relationship enables the prediction of operating conditions for mixing in a stirred tank reactor up to 10 L from shaken MTPs with 200 µL working volume. This granted a scale-up factor of 50.000, leading to a significant reduction of material and time consumption during process development and makes prediction of conditions more robust compared to the current approaches.

Scaling‐up of an Insect Cell‐based Virus Production Process in a Novel Single‐use Bioreactor with Flexible Agitation

AbstractA novel single‐use bioreactor was recently introduced to the market that is agitated by impellers suspended on flexible ropes rather than a rigid shaft. Computational fluid dynamics (CFD) models were created and validated by particle image velocimetry (PIV) to predict the bioreactor's fluid flow and mixing. The data were then used to scale‐up a Spodoptera frugiperda, subclone 9 (Sf9) insect cell‐based production of recombinant adeno‐associated virus (AAV) from a benchtop glass bioreactor to the single‐use system with 30 L working volume. This viral vector is one of the most commonly used in gene therapies. The volumetric power input was kept constant while maintaining reasonable mixing times and shear stresses between the scales. Peak cell densities of up to 7.2 × 106 cells mL−1 and maximum virus titers of 1.7 × 1011 vg mL−1 were achieved. Similar cell growth and metabolite profiles further proved the successful process transfer between the two geometrically non‐similar bioreactor systems. The pilot bioreactor yielded between 3.3 and 4.8 × 1015 vg that, depending on the therapy, can be sufficient for the treatment of a single patient.

Removal of methanol vapors in a jet-loop bioscrubber equipped with a venturi injector

A jet loop reactor equipped with a Venturi injector was used as a bioscrubber to treat air polluted with methanol. The oxygen transfer coefficient of the reactor was first characterized under abiotic conditions at different volumetric power inputs, ionic strengths and dynamic viscosities. The oxygen transfer coefficient (KLa) ranged 46.9–1272.82 h−1 with an actual volumetric power inputs from 3.6 to 21.5 kW m−3. Then, the reactor was inoculated with a mixed culture and applied for the treatment of air artificially polluted by methanol. Over 91 days, the actual volumetric power input was maintained at 11 kW m−3 and the KLa ranged from 720 to 860 h−1, while the volumetric loading rate was increased from of 5–60 g L−1 d−1 and the hydraulic residence time was increased from of 12–96 h. The volumetric methanol removal rate reached a maximum of 40.75 g L−1 d−1, at a removal efficiency of 67.6%. Under the optimal conditions tested, the microbial growth yield reached a minimum value of 0.11 g COD g−1 COD. These results suggest that high efficiency reactors such as the Venturi jet loop tested in the present work allow to reach high volumetric removal rates while maintaining low growth yield.

Characterization of hydrodynamics and volumetric power input in microtiter plates for the scale-up of downstream operations.

Parameter estimation for scale‐up of downstream operations from microtiter plates (MTPs) is mostly done empirically because engineering correlations between microplates and stirred tank reactors (STRs) are not yet available. It is challenging to change the operation mode from shaken MTPs to large‐scale STRs. For the scale‐up of STRs, volumetric power input is well‐established although it is unclear whether this parameter can be used to transfer the operations from MTPs. We determine the volumetric power input in MTPs via the temperature increase caused by the motion of the liquid. The hydrodynamics in MTPs are studied with computational fluid dynamics (CFD). Mixing is investigated in 96‐, 24‐, and 6‐well MTPs to cover different geometries, filling volumes, shaking diameters, and shaking frequencies. All CFD simulations are validated by experimental results, which now allows prediction of the volumetric power input and hydrodynamics at various conditions in MTPs without the need for further experiments. We provide a map of the power input achievable in MTPs. Based on this map, from knowing about large‐scale conditions, adequate microscale conditions can be adjusted for process development. This enables the direct scale‐up of downstream unit operations from MTPs to STRs.

Scaling-up of Haematococcus pluvialis production in stirred tank photobioreactor

The objective of this study was to evaluate three most common scale-up criteria for Haematococcus pluvialis production from cultivation bottles to 2 and 10 L of stirred tank PBRs. Constant volumetric power input (P/V) was found to be the most suitable criterion for H. pluvialis production. Total carotenoid amount per biomass concentration in 2 L and 10 L stirred tank PBRs were determined to be 4.57 mg/g and 4.77 mg/g, respectively. Antioxidant activity of total carotenoids extracted from H. pluvialis was also higher at constant P/V criterion where 46.91% inhibition rate with a total phenolic content of 11.76 mg gallic acid/L was achieved. Obtained results could be used to expand the bioproduction of H. pluvialis and its extracts in commercial scale.

Power consumption prediction in a coalescent liquid in mechanically agitated gas–liquid reactors

In mechanically agitated gas–liquid contactors design, transport characteristics such as volumetric mass transfer coefficients, power input, and gas hold-up often become the key parameters. Therefore, their values should be estimated as precisely as possible. The power input is usually used as the scale of energy dissipation for other characteristics. The goal of this work is to establish reliable power input correlations for industrial processes design, where the coalescent batch is used. The experiments were carried out in a pilot-plant and laboratory vessel. Different types of impellers, as well as their different diameters, were used, and also the combinations of radially and axially pumping impellers on a common shaft. Energy consumption was measured in a multi-impeller vessel with different impeller frequencies and several gas flows. Correlation equations describing the behavior of individual impellers were evaluated. The correlations we suggested can be used for impeller power prediction in industrial scale vessels under a wide range of operational conditions.

Analysis of liquid-to-gas mass transfer, mixing and hydrogen production in dark fermentation process

The aim of this work was to investigate mixing and liquid-to-gas mass transfer of hydrogen in relation to hydrogen production in the dark fermentation process as a function of agitation conditions and digestate viscosity. Experiments were carried out in a baffled mechanically-stirred reactor equipped with a dual-stage impeller using five levels of viscosity. Biohydrogen production was studied using glucose as substrate under controlled pH. Three experimental techniques, namely local conductimetry, chemical decolorization and Planar Laser Induced Fluorescence were used to measure mixing time tm and describe the flow pattern. The effects of inter-impeller clearance and tracer injection position were also studied. Then, kLaH2 was deduced from dynamic deaeration/aeration experiments. Experimental results showed that biohydrogen production presented a maximum in the transitional flow regime (Re about 200), and fell under turbulent flow (Re> 1000). Similarly, the evolution of kLaH2 was better described by Re than by the volumetric power input, contrary to literature data. Finally, the Damköhler number showed that hydrogen production was limited by liquid-to-gas mass transfer in the laminar regime and that maximum reaction rate could be reached only due to dissolved H2 supersaturation in the liquid phase. Conversely, the steep decrease of H2 production under turbulence conditions could be attributed neither to mass transfer, nor to mixing conditions, highlighting a probable negative interaction between turbulent eddies and biomass aggregates. Regarding kLa∙tm, the transitional flow region also approached ideal mixing, which strengthened the conclusion that H2 production was optimized in the transition region in the dark fermentation process.

Production and recovery of poly‐3‐hydroxybutyrate [P(3HB)] of ultra‐high molecular weight using fed‐batch cultures of Azotobacter vinelandii OPNA strain

AbstractBACKGROUNDPoly‐3‐hydroxybutyrate P(3HB) is a bioplastic that is characterized for its biodegradability and biocompatibility and can be used in the biomedical field. The aim of this study was to evaluate the scaling‐up process at pilot level, for the production and recovery of P(3HB) synthesized by Azotobacter vinelandii OPNA strain, based on the use of fed‐batch fermentation coupled to a recovery method using nonhalogenated solvents (ethanol and acetone).RESULTSIn fed‐batch cultivations at the 3‐L scale, using yeast extract and sucrose of industrial grade with a carbon:nitrogen ratio of 14 and manipulating the agitation rate from 500 to 700 rpm to give a maximal biomass concentration of 33.8 ± 1.5 g L−1, P(3HB) concentrations of 29 ± 4.5 g L−1 were reached. By simulating the gassed volumetric power input observed in the 3‐L bioreactors at the different agitation rates (500 and 700 rpm), a scaling‐up to 30‐L bioreactors was performed. At this scale, the P(3HB) concentration, and productivity were similar or even better than those values obtained at the smaller scale. The production process was coupled to a P(3HB) separation process, in which the polymer was precipitated with ethanol and washed with acetone, reaching a purity close to 95% and a yield of 85%. The P(3HB) obtained was of ultra‐high molecular mass, with values of 5693 ± 615 kDa.CONCLUSIONIn this study a successful scaling‐up process for the production of P(3HB) of ultra‐high molecular weight at pilot scale was developed. © 2019 Society of Chemical Industry

LA POTENCIA VOLUMÉTRICA COMO UN PARÁMETRO CONFIABLE PARA EL ESCALAMIENTO DE MATRACES AGITADOS A BIORREACTOR DE TANQUE AGITADO: PRODUCCIÓN DE UNA GLICOPROTEINA RECOMBINANTE POR Streptomyces lividans

In Streptomyces lividans, filamentous morphology varies according to hydrodynamics/aeration culture conditions, playing important roles in the production, secretion, and post-translational modification of recombinant glycoproteins. Volumetric power input (P/V) is normally used to scale-up bioprocesses. Here, we analyzed the effect of P/V on S. lividans growth and morphology as well as the production and O-mannosylation of the recombinant glycoprotein APA from Mycobacterium tuberculosis. Previously, we measured the P/V in conventional normal (NF, 0.20 kW/m3) and coiled (CF, 0.44 kW/m3) shake flasks. Here, these P/V were matched in 1.0 L bioreactors by adjusting the stirring speed. Similar specific growth rates were observed between shake flask and bioreactor cultures. In addition, similar rAPA yields (~25%) were observed in both the bioreactor and NF cultures, but these were lower than the yield in the CF culture (~36%). Furthermore, up to seven mannose residues were attached to the C-terminal of rAPA in both bioreactor cultures, which was one more than in the NF and CF cultures. However, at similar P/V, the morphology and biomass kinetics of growth were not similar. Our data indicate that scaling-up the production of recombinant glycoproteins using S. lividans by matching the P/V can be successful in terms of some, but not all stequeometric parameters, suggesting that the cellular responses could be differently affected by hydrodynamics/aeration differences between shake flasks and bioreactors.

Establishment of a CFD-based kL a model in microtiter plates to support CHO cell culture scale-up during clone selection.

Microtiter plates are a common tool for clone selection in biopharmaceutical development. A way of visualizing and evaluating these systems and key processes parameters is the application of Computational Fluid Dynamics (CFD). CFD is a powerful tool for the modelling of hydrodynamics and mass transfer parameters. In this work, CFD was used to determine the specific surface area, the volumetric power input and the oxygen mass transfer coefficient kL a for two different microtiter plates with different scales (100 μL - 5 mL). For this purpose, a new method of predicting the kL a is presented and calibrated with literature data. Scaling effects in shaken microtiter plates are evaluated by comparing two culture volume scales under various operating conditions. To test validity of these models, three different Boehringer Ingelheim Pharma proprietary CHO production cell lines with different growth characteristics were cultivated using the respective microtiter plates under different conditions until limitations in growth and viability were observable. The cell culture data then was compared to different parameters obtained by CFD. The calculated kL a values match the cell culture performance in the 96-deepwell by predicting lowered oxygen transfer with increasing culture volume and decreasing orbital velocity. The same cells behave differently in the 6-deepwell scale. Here, the overall larger shear stress might cause physical stress for the cells. The kL a model predicts overall higher shear rates for this system, supporting the experimental findings. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 2018.

Multiphase microreactors with intensification of oxygen mass transfer rate and mixing performance for bioprocess development

This research is focused on the development of a borosilicate glass-based microbioreactor (MBR) to address two of the challenges that MBRs may be confronted with: poor mixing and mass transfer limitations. To overcome these challenges, a microbubble column-bioreactor (μBC) for biotechnological research was developed and characterized. Pressurized air was supplied through a nozzle (hydraulic diameter 26 μm) at the bottom of the μBC (reactor volume 60 μL). The airflow was accelerated, generating a continuous stream of microbubbles that rose through the μBC. This investigation describes the hydrodynamic and mass transfer characterization of the μBC. The aim of the study was to prove that the pneumatic aeration through a micro nozzle provided sufficient aeration to satisfy the high demand of oxygen of aerobic bioprocesses, and at the same time, it enabled the homogenization of the cultivation broth and avoided the cell sedimentation. For this, the influence of the superficial gas velocity on the volumetric liquid-phase mass transfer coefficient is shown as well as the influence on other mass transport-related parameters, e.g. gas hold-up, Sauter mean bubble diameter, bubble rise velocity, superficial liquid velocity, volumetric power input, and mixing time. Additionally, a simplified computational fluid dynamic model was developed as a complement to this experimental research. The model serves as a supporting numerical tool to estimate the fluid dynamics inside the μBC.

Transcriptome analysis for the scale-down of a CHO cell fed-batch process

Transcriptome and metabolism analysis were performed to evaluate the scale-down of a CHO cell fed-batch process from a 10 L bioreactor to an ambr 15® (ambr) system. Two different agitation scale-down principles were applied, resulting in two different agitation rates in the ambr system: 1300 RPM based on the agitator tip speed, and 800 rpm based on the volumetric power input (P/V). Culture performance including cell growth, product titer, glycosylation, and specific consumption/production rates of metabolites was the same for both agitation rates in the ambr and was comparable to that of the 10 L system. The initial variation in gene expression between the inocula for the ambr and 10 L system was no longer present after three days of culture, indicating comparable culture conditions in both systems. Based on principal component analysis, changes in gene expression over time were similar between both scales with less than 6% variation. 2455 genes were uniquely regulated in the ambr system compared to 1604 genes in the 10 L system. Functional analysis of these genes did not reveal their relations with scale or cellular function. This study further strengthens that the ambr system gives representative culture performance for the 10 L bench-scale bioreactor.

Impact of nozzle operation on mass transfer in jet aerated loop reactors. Characterization and comparison to an aerated stirred tank reactor.

The impact of mass transfer on productivity can become a crucial aspect in the fermentative production of bulk chemicals. For highly aerobic bioprocesses the oxygen transfer rate (OTR) and productivity are coupled. The achievable space time yields can often be correlated to the mass transfer performance of the respective bioreactor. The oxygen mass transfer capability of a jet aerated loop reactor is discussed in terms of the volumetric oxygen mass transfer coefficient kLa [h-1] and the energetic oxygen transfer efficiency E [kgO2kW-1h-1]. The jet aerated loop reactor (JLR) is compared to the frequently deployed aerated stirred tank reactor. In jet aerated reactors high local power densities in the mixing zone allow higher mass transfer rates, compared to aerated stirred tank reactors. When both reactors are operated at identical volumetric power input and aeration rates, local kLa values up to 1.5 times higher are possible with the JLR. High dispersion efficiencies in the JLR can be maintained even if the nozzle is supplied with pressurized gas. For increased oxygen demands (above 120 mmolL-1h-1) improved energetic oxygen transfer efficiencies of up to 100 % were found for a JLR compared to an aerated stirred tank reactor operating with Rushton turbines.