New jet-aeration system using ‘Supercavitation’

Large‐scale animal cell operation is costly both in terms of facilities and consumables. Hence developmental studies with animal cells normally start at laboratory scale, often using small stirred tanks. In order to better optimise cell performance, it is necessary to know the physical conditions under which the cells are grown. In this study a laboratory‐scale vessel (2 dm3 working volume) with two large‐bladed paddle impellers was characterised hydrodynamically. Three different aeration methods (surface, sparging and membrane aeration) were investigated and compared. Power input and oxygen transfer rates to culture medium were determined as a function of agitation and gas flow rates. Non‐dimensional correlations were established for each case, which can be useful for scale‐up purposes. The results obtained indicate that power input is quite dependent on the vessel accessories: for the same agitation rate, the maximum power is required for the membrane structure and the minimum for surface aeration, with the addition of the sparger leading to an intermediate situation. Predictions found in the literature can be used for simple vessels, but may not be applicable when accessories are added to the vessel structure; in such cases, the use of experimental relationships are required. Oxygen transfer rate was dependent on the aeration method and working conditions (agitation and gas flow rates), particularly for sparger aeration. Membrane aeration gave larger oxygen transfer but higher gas pressure and flow rates were required. Surface aeration was the least effective method, nevertheless requiring gas flow rates similar to those used for membrane aeration. The aeration method of choice depends upon the culture and work specificities: surface aeration is limited to small cell concentrations and low oxygen consumption rates. For higher cell concentrations and oxygen consumption rates, both membrane and sparger aeration methods can be applied: the use of the sparger is limited to cells that are not affected by the presence of bubbles or the addition of surfactants, whereas the membrane aeration basket should not be used when a hydrodynamically controlled stirred tank is required.

Hydrodynamic effect of dispersed phase fraction on the mass transfer and uptake rate of hexadecane by an oil-degrading microbial consortium in an airlift bioreactor

Oxygen transfer rates were determined in a bubble aerated animal cell bioreactor. It was found that the oxygen transfer rates increased in the following order: large bubbles ( approximately 5 mm diameter) < intermediate bubbles ( approximately 1 mm diameter) < micron-sized bubbles ( approximately 100 microm diameter). Under certain conditions, the micron-sized bubbles were capable of achieving oxygen transfer rate up to 100 h(-1), a 10-20-fold higher transfer rate than the large bubbles. The effects of medium composition on oxygen transfer rates were different for the three ranges of bubbles studied. For the large bubbles, oxygen transfer rates decreased with increasing medium complexity. The lowest oxygen transfer rate was found in new-born calf serum (NBCS) and/or Pluronic F-68 supplemented media. For the intermediate and micron-sized bubbles, supplementation with NBCS into the culture media resulted in decreased oxygen transfer rate. However, further supplementation with Pluronic F-68 enhanced oxygen transfer rate greatly for both types of bubbles. The highest oxygen transfer rate was found for micron-sized bubbles in Pluronic F-68 supplemented media containing antifoam agent and NBCS.

Cultivations of mammalian cells are routinely conducted in shake flasks. In contrast to instrumented bioreactors, reliable options for non-invasive, time-resolved monitoring of the culture status in shake flasks are lacking. The Respiration Activity Monitoring Respiration Activity Monitoring System system was used to determine the oxygen transfer rate (OTR) in shake flasks. It was proven that the OTR could be regarded as equal to the oxygen uptake rate as the change of the dissolved oxygen concentration in the liquid phase over time was negligibly small. Thus, monitoring the oxygen transfer rate (OTR) was used to increase the information content from shake flask experiments. The OTR of a Chinese hamster ovary cell line was monitored by applying electrochemical sensors. Glass flasks stoppered with cotton plugs and polycarbonate flasks stoppered with vent-caps were compared in terms of mass transfer characteristics and culture behavior. Similar mass transfer resistances were determined for both sterile closures. The OTR was found to be well reproducible within one experiment (standard deviation <10%). It correlated with changes in cell viability and depletion of carbon sources, thus, giving more profound insights into the cultivation process. Culture behavior in glass and polycarbonate flasks was identical. Monitoring of the OTR was applied to a second culture medium. Media differed in the maximum OTR reached during cultivation and in the time when all carbon sources were depleted. By applying non-invasive, parallelized, time-resolved monitoring of the OTR, the information content and amount of data from shake flask experiments was significantly increased compared to manual sampling and offline analysis. The potential of the technology for early-stage process development was demonstrated.

The mass transfer analysis of the oxygen transfer performance of diffused air or subsurface mechanical aeration systems has progressed very little over the past 20 years. The recently‐developed ASCE Standard method for determination of the oxygen mass transfer performance of diffused or subsurface aeration systems is based on a greatly over‐simplified mass transfer model. Although the ASCE Standard can be used to empirically evaluate point performance conditions, it does not provide a meaningful representation of the actual mass transfer process and is not capable of accurately assessing or predicting performance under changing operating or environmental conditions. A new oxygen mass transfer model has been developed which is a fundamentally more rigorous description of the actual mass transfer process in diffused aeration systems. This model can be confidently used to predict aerator performance under changing operating and environmental conditions. The model is easily adapted to numerical computer solution for routine aeration systems performance evaluation as well as process design.

Two-fluids RANS predictions of gas cavities, power consumption, mixing time and oxygen transfer rate in an aerated fermenter scale-down stirred with multiple impellers

Oxygen transfer by orbital shaking of square vessels and deepwell microtiter plates of various dimensions

Specific features of the kinetics of alkane and alkylbenzene oxidation with HOONO formed in the H2O2-NaNO2 system (pH 4.27) are quantitatively explained assuming the simultaneous occurrence of reactions in the gas and liquid phases. A model of the kinetic distribution method is developed and verified that accounts for the equilibrium distribution of a substrate and a reagent between phases and their interaction in both phases. Relative rate constants for the oxidation ofn-alkanes (C3-C8), isobutane, cyclopentane, cyclohexane, benzene, and alkylbenzenes are measured over a wide range of the volume ratios of the gas and liquid phases (λ = Vg/V1). Relative rate constants for the oxidation of alkanes in the gas phase and alkylbenzenes in gas and solution were determined. Similarity in substrate selectivities and kinetic isotope effects of the gasphase reactions of alkanes and arenes with peroxynitrous acid and•OH radicals suggest that hydroxyl radical or the ˙OH...NO2 radical pair is an active species in the gas phase. In solution, alkylbenzenes react nonselectively with HOONO, as well as with ˙OH radicals. In contrast to the liquid-phase oxidation of arenes, the liquidphase oxidation of all alkanes under study insignificantly contribute (5–15%) to the overall rate of the substrate consumption.

Rates of oxygen transfer from air bubbles to aqueous NaCl solutions at various temperatures

Background2,3-Butanediol (BD) is a largely used fossil-based platform chemical. The yield and productivity of bio-based BD fermentative production must be increased and cheaper substrates need to be identified, to make bio-based BD production more competitive. As BD bioproduction occurs under microaerobic conditions, a fine tuning and control of the oxygen transfer rate (OTR) is crucial to maximize BD yield and productivity. Very few studies on BD bioproduction focused on the use of non-pathogenic microorganisms and of byproducts as substrate. The goal of this work was to optimize BD bioproduction by the non-pathogenic strain Bacillus licheniformis ATCC9789 by (i) identifying the ranges of volumetric and biomass-specific OTR that maximize BD yield and productivity using standard sugar and protein sources, and (ii) performing a preliminary evaluation of the variation in process performances and cost resulting from the replacement of glucose with molasses, and beef extract/peptone with chicken meat and bone meal, a byproduct of the meat production industry.ResultsOTR optimization with an expensive, standard medium containing glucose, beef extract and peptone revealed that OTRs in the 7–15 mmol/L/h range lead to an optimal BD yield (0.43 ± 0.03 g/g) and productivity (0.91 ± 0.05 g/L/h). The corresponding optimal range of biomass-specific OTR was equal to 1.4–7.9 {text{mmol}}_{{{text{O}}_{2} }} /{text{g}}_{text{CDW}} /{text{h}}, whereas the respiratory quotient ranged from 1.8 to 2.5. The switch to an agro-industrial byproduct-based medium containing chicken meat and bone meal and molasses led to a 50% decrease in both BD yield and productivity. A preliminary economic analysis indicated that the use of the byproduct-based medium can reduce by about 45% the BD production cost.ConclusionsA procedure for OTR optimization was developed and implemented, leading to the identification of a range of biomass-specific OTR and respiratory quotient to be used for the scale-up and control of BD bioproduction by Bacillus licheniformis. The switch to a byproduct-based medium led to a relevant decrease in BD production cost. Further research is needed to optimize the process of BD bioproduction from the tested byproduct-based medium.

The mass transfer rates of oxygen from air bubbles into both reverse osmosis (RO) and salt water (2.85% NaCl by mass) inside a baffled, well-mixed vessel have been investigated. Low aeration rates and impeller speeds were selected according to the Central Composite Rotatable Design (CCRD) experimental design approach. Empirical correlations with less than ±3% average prediction errors have been developed. Using identical operating conditions, the rate of oxygen transfer into pure RO water was significantly faster than that into salt water, with mass transfer coefficients ranging between 5.6 and 16.3 1/h for RO water and 4.4 and 14.7 1/h for salt water. The lower rates of oxygen transfer for salt water are hypothesized to be due to increased viscosity and correspondingly reduced diffusion in the boundary layer.

Azotobacter vinelandii OP is a bacterium that produces poly(3-hydroxybutyrate) (PHB). PHB production in a stirred bioreactor, at different oxygen transfer strategies, was evaluated. By applying different oxygen contents in the inlet gas, the oxygen transfer rate (OTR) was changed under a constant agitation rate. Batch cultures were performed without dissolved oxygen tension (DOT) control (using 9% and 21% oxygen in the inlet gas) and under DOT control (4%) using gas blending. The cultures that developed without DOT control were limited by oxygen. As result of varying the oxygen content in the inlet gas, a lower OTR (4.6mmolL-1h-1) and specific oxygen uptake rate (11.6mmolg-1h-1) were obtained using 9% oxygen in the inlet gas. The use of 9% oxygen in the inlet gas was the most suitable for improving the intracellular PHB content (56 ± 6w w-1). For the first time, PHB accumulation in A. vinelandii OP cultures, developed with different OTRs, was compared under homogeneous mixing conditions, demonstrating that bacterial respiration affects PHB synthesis. These results can be used to design new oxygen transfer strategies to produce PHB under productive conditions.

Oxygen mass transfer limitations set the performance boundaries of microbial PHA production processes – A model-based problem investigation supporting scale-up studies

Biocatalytic oxidation reactions employing molecular oxygen as the electron acceptor are difficult to conduct in a continuous flow reactor because of the requirement for high oxygen transfer rates. In this paper, the oxidation of glucose to glucono-1,5-lactone by glucose oxidase was used as a model reaction to study a novel continuous agitated cell reactor (ACR). The ACR consists of ten cells interconnected by small channels. An agitator is placed in each cell, which mixes the content of the cell when the reactor body is shaken by lateral movement. Based on tracer experiments, a hydrodynamic model for the ACR was developed. The model consisted of ten tanks-in-series with back-mixing occurring within and between each cell. The back-mixing was a necessary addition to the model in order to explain the observed phenomenon that the ACR behaved as two continuous stirred tank reactors (CSTRs) at low flow rates, while it at high flow rates behaved as the expected ten CSTRs in series. The performance of the ACR was evaluated by comparing the steady state conversion at varying residence times with the conversion observed in a stirred batch reactor of comparable size. It was found that the ACR could more than double the overall reaction rate, which was solely due to an increased oxygen transfer rate in the ACR caused by the intense mixing as a result of the spring agitators. The volumetric oxygen transfer coefficient, kL a, was estimated to be 344 h-1 in the 100 mL ACR, opposed to only 104 h-1 in a batch reactor of comparable working volume. Interestingly, the large deviation from plug flow behavior seen in the tracer experiments was found to have little influence on the conversion in the ACR, since both a plug flow reactor (PFR) model and the backflow cell model described the data sufficiently well. Biotechnol. Bioeng. 2017;114: 1222-1230. © 2017 Wiley Periodicals, Inc.

Thermodynamic and Gasdynamic Aspects of a Boiling Liquid Expanding Vapour Explosion