Volumetric Oxygen Mass Transfer Coefficient Research Articles

Mimicking Marine Conditions to Improve Prodigiosin Yields in Bioreactor

Prodigiosin is a red bacterial pigment with great potential as a natural dye and drug precursor, while presenting several pharmacological properties, including antimicrobial and anticancer activities. Its commercialization for biomedical applications, however, remains scarce. The major limitations are related to the lack of efficient bioprocesses and scaling up from laboratory to production. In the present work, the upstream process for prodigiosin production was developed using a marine Serratia rubidaea isolated from a sample collected near a shallow-water hydrothermal vent. The yield of product per biomass was found to be influenced by the cell concentration in the inoculum. The system was scaled up to 2 L stirred tank reactors with two different vessel geometries. It was shown that the vessel geometry and a cascade control mode for regulating the dissolved oxygen concentration influenced the volumetric oxygen mass transfer coefficient (kLa) and thus prodigiosin production. To improve product yields, strategies to mimic the aeration conditions found at the sampling site were tested. When the inoculum was grown for 5 h at 200 rpm and for 19 h at 25 rpm, which significantly decreased the oxygen available, the cells produced 588.2 mgproduct/gbiomass, corresponding to a production of 1066.2 mg of prodigiosin in 24 h and a productivity of 36.1 mgproduct/(L.h). This is a 3.7-fold increase in prodigiosin yield and a 4.5-fold increase in productivity in relation to when no particular strategy was promoted. Additionally, it was shown that lipid analysis and flow cytometry may be used as reliable at-line analytical tools, allowing the monitoring of cell condition and prodigiosin production during fermentation.

Population balance modeling-assisted prediction of oxygen mass transfer coefficients with optical measurements

Prediction of bubble size distributions (BSD) is challenging but necessary to develop a more advanced bubble population-based model for oxygen mass transfer with increased data quality while reducing the required experimental effort. In this paper, we experimentally investigated bubble sizes in a pilot-scale setup using a submersible in-situ flow-microscope. This technique enables bubble size measurements in dense bubbly flows and at airflow rates of up to 40 sL/min above the diffuser, where former measurement methods were limited to a range below 8 slpm with a comparable diffuser configuration. The data obtained were used to study coalescence and breakup behavior and to predict bubble size distributions using population balance modeling (PBM). We also investigated the prediction of the volumetric oxygen mass transfer coefficient based on measurement of bubble size at only one height in combination with PBM to provide reliable estimates of the apparent mass transfer rate with less experimental effort. A mass transfer rate estimate was obtained with deviations from the experimentally determined mass transfer rate of <10 %.

Advancing aerobic digestion efficiency using ultrafine bubbles in wastewater treatment

The application of ultrafine/nanobubbles (NBs) was tested as an aeration mechanism in a laboratory scale, semi-batch, biological wastewater treatment unit and compared with a similar scale, conventional bubbling supported aerobic digestion unit. The results showed that the oxygen utilization rate (OUR) and volumetric oxygen mass transfer coefficient (kla) were doubled from 0.075 to 0.159 mg O2/min and 0.07 to 0.13 respectively, through the application of NBs compared to the use of conventional bubbles (CBs). This was achieved by exploiting the sufficient residence time NBs can have in the aqueous system along with its capacity of high mass transfer surface area to volume ratio. The twofold increment in the OUR and kla due to the application NBs improved the biodegradation rate of the organic matter from 5.83 to 17.5 mg/l.hr compared to the application of CBs. Thus, 60 % of the hydraulic residence time reduction was achieved by the application NBs compared to CBs to achieve a similar amount of organic waste degradation. Moreover, the membrane filtration results also showed a reduction in the sludge load and fouling rate for aerobic membrane bioreactors supported by NB systems. A possible mechanism for sludge reduction was also proposed based on the results achieved.

Preparation of Free-Surface Hyperbolic Water Vortices.

Free surface vortices are present in industry in flow regulation, energy dissipation, and energy generation. Although investigated extensively, detailed experimental data regarding free surface vortices are lacking, particularly regarding the turbulence at the interface. The present paper reports on a special type of free surface vortex first proposed by Walter Schauberger in the 1960s that has an oxygen volumetric mass transfer coefficient exceeding the value of similar systems. This special type of vortex forms in a hyperbolic funnel. Different stable regimes can be stabilized with different hydraulic characteristics. Other advantages of this technology are its energy efficiency, simple design, and scalability. The flow in this hyperbolic funnel is characterized by strong turbulence and an increased surface area of the air-water interface. The local pressure strongly varies along the surface, resulting in a pronounced wavey air-water boundary layer. Due to the helical flow, these perturbations move inward, pulling the boundary layer with them. The resultant pressure gradient draws a certain air volume into the water vortex. The construction of the basic hyperbolic funnel setup and operational examples, including high-speed visualization for three different stable regimes, are presented in this work.

Minimally-disruptive method to estimate the volumetric oxygen mass transfer coefficient (kLa) for recombinant Escherichia coli fermentations

In the biopharmaceutical industry, accurate prediction of the oxygen uptake rate (OUR) is critical to understanding cell health, where OUR is related to the oxygen transfer rate (OTR) and the culture dissolved oxygen (DO). Key to accurate OTR assessment is an accurate volumetric oxygen mass transfer coefficient (kLa) estimate, where kLa represents the oxygen driving force from gas to liquid phase. Common approaches to estimate kLa have significant limitations, such as disruptive to the culture by stopping the oxygen supply or the use of only cell-free buffered solution. Yet, it is well-known that cell secretions and additions (i.e., base and antifoam) can dramatically can affect kLa, and accumulate during the culture. This study describes a novel, minimally-disruptive method to estimate kLa by halving the gas flow rate periodically throughout the fermentation. This approach was used to estimate kLa at multiple times for two recombinant Escherichia coli strains cultured in ambr250 modular vessels. In one case, the duration of the halved gas flow was varied. In the second case, the effects of only cell secretions was examined. As the oxygen supply was only halved, the risk of culture loss was significantly lower compared to the dynamic gas-out method.

Scale-down of CHO cell cultivation from shake flasks based on oxygen mass transfer allows application of parallelized, non-invasive, and time-resolved monitoring of the oxygen transfer rate in 48-well microtiter plates.

Cultivating Chinese hamster ovary (CHO) cells in microtiter plates (MTPs) with time-resolved monitoring of the oxygen transfer rate (OTR) is highly desirable to provide process insights at increased throughput. However, monitoring of the OTR in MTPs has not been demonstrated for CHO cells, yet. Hence, a CHO cultivation process was transferred from shake flasks to MTPs to enable monitoring of the OTR in each individual well of a 48-well MTP. For this, the cultivation of an industrially relevant, antibody-producing cell line was transferred from shake flask to MTP based on the volumetric oxygen mass transfer coefficient (kL a). Culture behavior was well comparable (deviation of the final IgG titer less than 10%). Monitoring of the OTR in 48-well MTPs was then used to derive the cytotoxicity of dimethyl sulfoxide (DMSO) based on a dose-response curve in a single experiment using a second CHO cell line. Logistic fitting of the dose-response curve determined after 100h was used to determine the DMSO concentration that resulted in a cytotoxicity of 50% (IC50). A DMSO concentration of 2.70%±0.25% was determined, which agrees with the IC50 previously determined in shake flasks (2.39%±0.1%). Non-invasive, parallelized, and time-resolved monitoring of the OTR of CHO cells in MTPs was demonstrated and offers excellent potential to speed up process development and assess cytotoxicity.

Immobilization of mixed cells by Flaxseeds (Linum usitatissimum) extract as new nonconventional biocarrier for biodegradation of sodium dodecyl sulfate

Flaxseeds as a new nonconventional biocarrier was used for the first time to immobilize mixed bacterial cells for biodegradation of sodium dodecyl sulfate (SDS) in actual wastewaters. The results revealed that SDS elimination efficiency in domestic wastewater (DWW) and household detergents manufacturing wastewater (HWW) were 98.8% and 94.5%, respectively. The immobilized cells were repeatedly used for 60 batches without notable loss of their bioactivity, mechanical and chemical stability. Seven kinetic models were applied to depict the interrelation between cells growth and substrate consumption which were; Blackman, Monod, Haldane, Teissier, Moser, Han-Levenspiel, and Contois Models. Teissier model fit well the experimental data with lowest sum of squares error (SSE) of 2.41 × 10−14 indicating exponential growth of biocatalyst inside the biocarrier. Endogenous rate constant (Kd), and yield coefficient (Y) were found to be 0.0039 h−1, and 0.44 h−1, respectively. Values of first order rate constant (K1), effective diffusivity (De), mass transfer coefficient, effectiveness factor (η), and Thiele modulus (Φ) were found to be 1.55 × 10−5 s−1, 6.44×10−7 cm2/s, 2.14×10−6 cm/s, 0.88, and 0.49, respectively. Values of oxygen uptake rate (OUR), volumetric oxygen mass transfer coefficient (KLa) and oxygen transfer rate (OTR) were 0.0013 mg O2/L. s, 0.0222 s−1 and 0.00111 mg O2/L. s, respectively. Experimental and predicted results of (OUR) were in a good agreement with determination coefficient (R2) of 0.94.

Design and engineering characterization of a horizontal tubular bioreactor with spiral impeller for cell cultivation

Aerated stirred tank bioreactors (STRs) are the norm for commercial production of biologicals but tend to exert high shear forces from high impeller tip speeds, direct sparging, bubble disruption at the surface and foam formation. In this work, a novel 5 liter horizontal tubular bioreactor (HTB) fitted with a spiral impeller was designed for cell cultures. The abiotic and engineering characterization of the HTB was undertaken in terms of fluid flow pattern, mixing time (θm), minimum agitation speed Njs, volumetric oxygen mass transfer coefficient (kLa), and power consumption (P). The bioreactor showed optimum operability between 2 and 3 litre, and comparable mixing time ranges, power consumption and volumetric oxygen mass transfer coefficients (kLa) between 5 and 16 h−1 to a STR and other conventional systems. An ANOVA analysis disseminated that impeller immersion and mixing speeds had significant effects on mixing times, while aeration rates and mixing speeds significantly impacted kLa. The abiotic and engineering characterization investigations revealed that the bioreactor design supported good surface aeration with bubble entrainment for oxygen mass transfer while imparting low energy into the system, which are key attributes in promoting a low shear environment for cell culturing.

Enhanced production of amyrin in Yarrowia lipolytica using a combinatorial protein and metabolic engineering approach

BackgroundAmyrin is an important triterpenoid and precursor to a wide range of cosmetic, pharmaceutical and nutraceutical products. In this study, we metabolically engineered the oleaginous yeast, Yarrowia lipolytica to produce α- and β-amyrin on simple sugar and waste cooking oil.ResultsWe first validated the in vivo enzymatic activity of a multi-functional amyrin synthase (CrMAS) from Catharanthus roseus, by expressing its codon-optimized gene in Y. lipolytica and assayed for amyrins. To increase yield, prevailing genes in the mevalonate pathway, namely HMG1, ERG20, ERG9 and ERG1, were overexpressed singly and in combination to direct flux towards amyrin biosynthesis. By means of a semi-rational protein engineering approach, we augmented the catalytic activity of CrMAS and attained ~ 10-folds higher production level on glucose. When applied together, protein engineering with enhanced precursor supplies resulted in more than 20-folds increase in total amyrins. We also investigated the effects of different fermentation conditions in flask cultures, including temperature, volumetric oxygen mass transfer coefficient and carbon source types. The optimized fermentation condition attained titers of at least 100 mg/L α-amyrin and 20 mg/L β-amyrin.ConclusionsThe design workflow demonstrated herein is simple and remarkably effective in amplifying triterpenoid biosynthesis in the yeast Y. lipolytica.

Mass Transfer, Gas Holdup, and Kinetic Models of Batch and Continuous Fermentation in a Novel Rectangular Dynamic Membrane Airlift Bioreactor

Compared with conventional cylinder airlift bioreactors (CCABs) that produce coarse bubbles, a novel rectangular dynamic membrane airlift bioreactor (RDMAB) developed in our lab produces fine bubbles to enhance the volumetric oxygen mass transfer coefficient (kLa) and gas holdup, as well as improve the bioprocess in a bioreactor. In this study, we compared mass transfer, gas holdup, and batch and continuous fermentation for RNA production in CCAB and RDMAB. In addition, unstructured kinetic models for microbial growth, substrate utilization, and RNA formation were established. In batch fermentation, biomass, RNA yield, and substrate utilization in the RDMAB were higher than those in the CCAB, which indicates that dynamic membrane aeration produced a high kLa by fine bubbles; a higher kLa is more beneficial to aerobic fermentation. The starting time of continuous fermentation in the RDMAB was 20 h earlier than that in the CCAB, which greatly improved the biological process. During continuous fermentation, maintaining the same dissolved oxygen level and a constant dilution rate, the biomass accumulation and RNA concentration in the RDMAB were 9.71% and 11.15% higher than those in the CCAB, respectively. Finally, the dilution rate of RDMAB was 16.7% higher than that of CCAB during continuous fermentation while maintaining the same air aeration. In summary, RDMAB is more suitable for continuous fermentation processes. Developing new aeration and structural geometry in airlift bioreactors to enhance kLa and gas holdup is becoming increasingly important to improve bioprocesses in a bioreactor.

Numerical and Experimental Investigation of the Hydrodynamics in the Single-Use Bioreactor Mobius® CellReady 3 L.

Two-way Euler-Lagrange simulations are performed to characterize the hydrodynamics in the single-use bioreactor Mobius® CellReady 3 L. The hydrodynamics in stirred tank bioreactors are frequently modeled with the Euler–Euler approach, which cannot capture the trajectories of single bubbles. The present study employs the two-way coupled Euler–Lagrange approach, which accounts for the individual bubble trajectories through Langrangian equations and considers their impact on the Eulerian liquid phase equations. Hydrodynamic process characteristics that are relevant for cell cultivation including the oxygen mass transfer coefficient, the mixing time, and the hydrodynamic stress are evaluated for different working volumes, sparger types, impeller speeds, and sparging rates. A microporous sparger and an open pipe sparger are considered where bubbles of different sizes are generated, which has a pronounced impact on the bubble dispersion and the volumetric oxygen mass transfer coefficient. It is found that only the microporous sparger provides sufficiently high oxygen transfer to support typical suspended mammalian cell lines. The simulated mixing time and the volumetric oxygen mass transfer coefficient are successfully validated with experimental results. Due to the small reactor size, mixing times are below 25 s across all tested conditions. For the highest sparging rate of 100 mL min, the mixing time is found to be two seconds shorter than for a sparging rate of 50 mL min, which again, is 0.1 s longer than for a sparging rate of 10 mL min at the same impeller speed of 100 rpm and the working volume of 1.7 L. The hydrodynamic stress in this bioreactor is found to be below critical levels for all investigated impeller speeds of up to 150 rpm, where the maximum levels are found in the region where the bubbles pass behind the impeller blades.

CFD-Based and Experimental Hydrodynamic Characterization of the Single-Use Bioreactor XcellerexTM XDR-10.

Understanding the hydrodynamic conditions in bioreactors is of utmost importance for the selection of operating conditions during cell culture process development. In the present study, the two-phase flow in the lab-scale single-use bioreactor Xcellerex XDR-10 is characterized for working volumes from 4.5 L to 10 L, impeller speeds from 40 rpm to 360 rpm, and sparging with two different microporous spargers at rates from 0.02 L min to 0.5 L min. The numerical simulations are performed with the one-way coupled Euler–Lagrange and the Euler–Euler models. The results of the agitated liquid height, the mixing time, and the volumetric oxygen mass transfer coefficient are compared to experiments. For the unbaffled XDR-10, strong surface vortex formation is found for the maximum impeller speed. To support the selection of suitable impeller speeds for cell cultivation, the surface vortex formation, the average turbulence energy dissipation rate, the hydrodynamic stress, and the mixing time are analyzed and discussed. Surface vortex formation is observed for the maximum impeller speed. Mixing times are below 30 s across all conditions, and volumetric oxygen mass transfer coefficients of up to 22.1 h are found. The XDR-10 provides hydrodynamic conditions which are well suited for the cultivation of animal cells, despite the unusual design of a single bottom-mounted impeller and an unbaffled cultivation bioreactor.

Numerical and experimental characterization of the single-use bioreactor Xcellerex™ XDR-200

The optimization of operating conditions is vital for cell culture process development. In the present study, the pilot-scale single-use bioreactor Xcellerex™ XDR-200, which is typically used in cell culture scale-up, is investigated. This unbaffled reactor is equipped with an off-centered, bottom mounted impeller, and has a maximum working volume of 200 L. The flow field for this sparsely investigated bioreactor configuration is studied with computational fluid dynamics. Moreover, numerical simulations of the mixing time and the volumetric oxygen mass transfer coefficient for seven different test conditions are validated against experimental data. Mixing times across all tested conditions are found to remain below 30 s, and the volumetric oxygen mass transfer coefficient is between 2.0 and 20.0 h−1, which is a typical range for animal cell culture processes. These values of the oxygen transfer coefficient are found for as low as 0.004–0.125 L L−1 min−1 sparging rates with the microporous sparger. The hydrodynamic stress remains below critical values for cell damage for all conditions investigated. Vortex formation is suppressed in the bioreactor even though it is unbaffled due to off-centered impeller. Across the test conditions, the highest investigated impeller speed of 200 rpm is the most favorable due to fast mixing and high oxygen transfer.

Effect of the Concentration of Extracellular Polymeric Substances (EPS) and Aeration Intensity on Waste Glycerol Valorization by Docosahexaenoic Acid (DHA) Produced in Heterotrophic Culture of Schizochytrium sp

The study aimed to determine the effectiveness of docosahexaenoic acid (DHA) production by Schizochytrium sp. biomass fed with waste glycerol depending on the concentration of extracellular polymeric substances (EPS) in the culture medium and medium aeration effectiveness. The microalgae from the genus Schizochytrium sp. were proved to be capable of producing EPS composed of glucose, galactose, mannose, fucose, and xylose. The highest EPS concentration, reaching 8.73 ± 0.09 g/dm3, was determined at the stationary growth phase. A high EPS concentration caused culture medium viscosity to increase, contributing to diminished oxygen availability for cells, lower culture effectiveness, and reduced waste glycerol conversion to DHA. The Schizochytrium sp. culture variant found optimal in terms of the obtained technological effects and operating costs was performed at the volumetric oxygen mass transfer coefficient of kLa = 600 1/h, which enabled obtaining dry cell weight (DCW) of 147.89 ± 4.77 g/dm3, lipid concentration of 69.44 ± 0.76 g/dm3, and DHA concentration in the biomass reaching 29.44 ± 0.36 g/dm3. The effectiveness of waste glycerol consumption in this variant reached 3.76 ± 0.31 g/dm3·h and 3.16 ± 0.22 g/gDCW.

Influence of counterdiffusion effects on mass transfer coefficients in stirred tank reactors

Accurate knowledge of volumetric oxygen mass transfer coefficients in multiphase systems is important for successfully designing and efficient operation of process plants. As a result, a large number of papers on the determination of volumetric mass transfer coefficients kLa have been published in the literature. The dynamic degassing method is probably the most common method for determining the volumetric mass transfer coefficient. However, little work is known on the influence of countercurrent diffusion effects, arising from further dissolved components, on the volumetric mass transfer coefficient.For this reason, the effect of countercurrent diffusion is investigated in the present work by using different stripping gases to determine the volumetric oxygen mass transfer coefficient. Furthermore, the effect of counterdiffusion is investigated for both conventional aeration and aeration with microbubbles.The present work shows that the choice of stripping gas has a decisive influence on the determination of the volumetric oxygen mass transfer coefficient. Moreover, it can be shown that this effect is directly proportional to the solubility of the stripping gas in the aqueous phase. Simultaneous measurements of bubble size distributions allow determining mass transfer coefficients kL. A model is developed describing the decrease in the mass transfer coefficient as a function of the solubility of the stripping gas.Furthermore, it can be shown that for the experimental determination of volumetric oxygen mass transfer coefficients, the choice of stripping gas should be adapted to secondary gas types occurring within real processes achieving a better comparability.

Gas\u2013liquid mass transfer characteristics of aviation fuel scrubbing in an aircraft fuel tank

Dissolved oxygen evolving from aviation fuel leads to an increase in the oxygen concentration in an inert aircraft fuel tank ullage that may increase the flammability of the tank. Aviation fuel scrubbing with nitrogen-enriched air (NEA) can largely reduce the amount of dissolved oxygen and counteract the adverse effect of oxygen evolution. The gas–liquid mass transfer characteristics of aviation fuel scrubbing are investigated using the computational fluid dynamics method, which is verified experimentally. The effects of the NEA bubble diameter, NEA superficial velocity and fuel load on oxygen transfer between NEA and aviation fuel are discussed. Findings from this work indicate that the descent rate of the average dissolved oxygen concentration, gas holdup distribution and volumetric mass transfer coefficient increase with increasing NEA superficial velocity but decrease with increasing bubble diameter and fuel load. When the bubble diameter varies from 1 to 4 mm, the maximum change of descent rate of dissolved oxygen concentration is 18.46%, the gas holdup is 8.73%, the oxygen volumetric mass transfer coefficient is 81.45%. When the NEA superficial velocities varies from 0.04 to 0.10 m/s, the maximum change of descent rate of dissolved oxygen concentration is 146.77%, the gas holdup is 77.14%, the oxygen volumetric mass transfer coefficient is 175.38%. When the fuel load varies from 35 to 80%, the maximum change of descent rate of dissolved oxygen concentration is 21.15%, the gas holdup is 49.54%, the oxygen volumetric mass transfer coefficient is 44.57%. These results provide a better understanding of the gas and liquid mass transfer characteristics of aviation fuel scrubbing in aircraft fuel tanks and can promote the optimal design of fuel scrubbing inerting systems.

Influence of Interfacial Force Models and Population Balance Models on the kLa Value in Stirred Bioreactors

Optimal oxygen supply is vitally important for the cultivation of aerobically growing cells, as it has a direct influence on cell growth and product formation. A process engineering parameter directly related to oxygen supply is the volumetric oxygen mass transfer coefficient kLa. It is the influences on kLa and computing time of different interfacial force and population balance models in stirred bioreactors that have been evaluated in this study. For this investigation, the OpenFOAM 7 open-source toolbox was utilized. Firstly, the Euler–Euler model with a constant bubble diameter was applied to a 2L scale bioreactor to statistically examine the influence of different interfacial models on the kLa value. It was shown that the kL model and the constant bubble diameter have the greatest influence on the calculated kLa value. To eliminate the problem of a constant bubble diameter and to take effects such as bubble breakup and coalescence into account, the Euler–Euler model was coupled with population balance models (PBM). For this purpose, four coalescence and five bubble breakup models were examined. Ultimately, it was established that, for all of the models tested, coupling computational fluid dynamics (CFD) with PBM resulted in better agreement with the experimental data than using the Euler–Euler model. However, it should be noted that the higher accuracy of the PBM coupled models requires twice the computation time.

Effect of the volumetric oxygen mass transfer coefficient on producing δ-endotoxins by Bacillus thuringiensis in culture medium based on forage palm

Bacillus thuringiensis is the main commercial source of safe insecticidal toxins. On the industrial scale, oxygenation is the most important variable for enhancing the production of δ-endotoxin by B. thuringiensis and improving its toxicity. Therefore, the parameters of growth kinetics, the formation of spores, the production of δ-endotoxin, and its toxicity against Spodoptera frugiperda were evaluated in batch cultures of B. thuringiensis cultivated in a culture medium based on forage palm with different KLα values. In all conditions, diauxic growth curves were observed due to the change of carbon source. Maximum cell concentration increased when KLα values were raised from 11 to 16 h−1, but biomass productivity was enhanced only when KLa was increased from 11 to 13 h−1. Due to the diauxic growth, spore production and δ-endotoxin production were observed at two different times. The first peak was generally lower than the second peak. At both peaks, a high concentration of spores was reached using a KLa of 13 h−1, but the highest production of δ-endotoxin and the maximum toxin yield based on spores or substrate were observed in the KLa of 16 h−1. Therefore, a bioassay against S. frugiperda was performed using δ-endotoxin produced under a KLa of 16 h−1. Although more δ-endotoxin was produced in the second peak than in the first peak, the highest toxicity was observed with toxins produced in the first peak. These results suggest that the KLα affects the production of δ-endotoxin and that toxicity against S. frugiperda decreases when fermentation time is increased.

Numerical modelling of oxygen mass transfer in diffused aeration systems: A CFD-PBM approach

The diffused aeration process is the most energy-intensive operation of bioreactor treatment, amounting to 45–75 % of the plant energy costs. To improve its efficiency, it is essential to measure the oxygen transfer rate from the aerators to wastewater. In this study, a multiphase mixture computational fluid dynamics (CFD) model is developed using k-ε turbulence closure equations along with a discrete population balance model (PBM) add-on with specific bubble classes, to predict the oxygen mass transfer. The transfer of oxygen species from air to water is modeled using the species transport model. The PBM is used to analyze the formation, growth, breakage, and coalescence of air bubbles. The validated model is then extended for sensitivity analysis for a diffused aeration system in a bench-scale aeration tank. Results show that, the volumetric oxygen mass transfer coefficient increases by 15 %, with a decrease of air bubble size by 10 %. The air bubbles have a wider distribution, with a larger diameter near the bottom of the bioreactor and a narrow distribution with a smaller bubble size at the top. Results show that, in the bioreactor, the dissolved oxygen concentration reaches the equilibrium or saturation value when the height by breadth ratio is 2.5 and does not increase further with increase in height of the water column. Also, the air bubble size of 6 mm was the efficient bubble size for a fixed airflow rate of 1.45 m3 h−1.

Does the BioBLU 0.3f single-use scale to the BioFlo\xae 320 reuseable bioreactor on a matched volumetric oxygen mass transfer coefficient?

The volumetric oxygen mass transfer coefficient (k_{l} a) is an essential parameter in aerobic high-cell density fermentation where the availability of oxygen to growing microorganisms is a limiting factor. Bioprocess teams looking to scale-up/down between the Eppendorf BioBLU 0.3f single-use vessel and the BioFlo® 320 reusable vessel bioreactors may find it challenging using a matched k_{l} a. The maximum k_{l} a of the BioFlo® 320 reusable bioreactor was 109 h−1, which was approximately twice that of the BioBLU 0.3f single-use vessel. The results here show no overlap in k_{l} a values when both bioreactors were compared and thus conclude that scalability based on k_{l} a is not viable. The maximum k_{l} a of the Eppendorf BioBLU 0.3f single-use reported here was 47 h−1 compared to that of the manufacturer’s value of 2500 h−1, indicating a 53-fold difference. This discrepancy was attributed to the incompatible sulfite addition method used by the manufacturer for estimation.