Oxygen Mass Transfer Coefficient Research Articles

Hydrodynamics and mass transfer in miniaturized bubble column bioreactors.

Miniaturized bubble columns (MBCs) have different hydrodynamics in comparison with the larger ones, but there is a lack of scientific data on MBCs. Hence, in this study, the effect of gas hold-up, flow regimes, bubble size distribution on volumetric oxygen mass transfer coefficient at different pore size spargers and gas flow rates in MBCs in the presence and absence of microorganisms were investigated. It was found that flow regime transition occurred around low gas flow rates of 1.18 and 0.85cm/s for small (16-40µm) and large (40-100µm) pore size spargers, respectively. Gas hold-up and KLa in MBC with small size sparger were higher than those with larger one, with an increasing effect in the presence of microorganisms. A comparison revealed that the wall effect on the flow regime and gas hold-up in MBCs was greater than bench-scale bubble columns. The KLa values significantly increased up to tenfold using small pore size sparger. In the MBC and stirred tank bioreactors, the maximum obtained cell concentrations were OD600 of 41.5 and 43.0, respectively. Furthermore, it was shown that in MBCs, higher KLa and lower turbulency could be achieved at the end of bubbly flow regime.

Mass Transfer Performance of a String Film Reactor: A Bioreactor Design for Aerobic Methane Bioconversion

The mass transfer performance of a string film reactor (SFR)—a bioreactor design for the aerobic bioconversion of methane—was investigated. The results showed that the SFR could achieve high mass transfer performance of gases, and the highest values of the mass transfer coefficients for oxygen and methane were 877.1 h−1 and 408.0 h−1, respectively. There were similar mass transfer coefficients for oxygen and methane in absorption experiments using air, methane, and air–methane mixed gas under the same liquid flow rate conditions, implying that each gas is delivered into the liquid without mutual interaction. The mass transfer performance of the SFR was significantly influenced by the liquid flow rate and the hydrophilicity of the string material, whereas the magnitude of the gas flow rate effect on the mass transfer performance depended on both the tested liquid flow rate and the gas flow rate. Furthermore, the mass transfer performance of the SFR was compared with those of other types of 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.

Porous polymer derived ceramic (PDC)-montmorillonite-H3PMo12O40/SiO2 composite membranes for microbial fuel cell (MFC) application

Ceramic membranes can serve as viable alternatives to the less mechanically stable polymeric membranes utilized in microbial fuel cells (MFCs). In this work, a series of polymer-derived ceramic (PDC) proton exchange composite membranes with large ion exchange capacity (IEC) values, high cation transport numbers, and low oxygen diffusion coefficients have been synthesized at various pyrolysis temperatures using a pressing technique. These materials were composed of a polysiloxane matrix mixed with proton-conducting fillers such as montmorillonite and H3PMo12O40/SiO2 at different ratios. By tuning the average pore sizes of the membranes between 0.1 and 1 µm and their hydrophilic/hydrophobic characteristics, the maximum IEC of 0.6072 mequiv/g and cation transport number of 0.6988 were obtained, which is 67% and 72% of polymeric nafion performance, respectively. In addition, the minimal oxygen mass transfer coefficient achieved by this approach was equal to 5.62 × 10−4 cm/s, which is very close to the commercial nafion membrane value. The fabricated PDC composite membranes meet all the essential criteria required for their use in MFC applications and represent a high potential to overcome limitations of polymeric membrane.

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.

An innovative bioprocess for methane conversion to methanol using an efficient methane transfer chamber coupled with an airlift bioreactor

Biosynthesis of methanol from methane as a direct method takes place at ambient temperature and pressure which causes a considerable reduction in process costs. In this study an efficient methane transfer chamber along with an external-loop airlift bioreactor were developed to dissolve methane and oxygen in the culture separately. Mass transfer coefficients for oxygen in the bioreactor and methane in the transfer chamber were obtained 97.2h−1 and 70.8h−1 respectively. Two strains of methanotroph bacteria (AS1 and AS2) were also isolated from activated sludge. Factorial design of experiments for operational parameters showed a maximum productivity for AS1 strain at 28°C when using nitrate as nitrogen source. Batch runs in airlift bioreactor using the AS1 strain and optimized operating parameters represented a peak of 1600mg/L in methanol synthesis during the first 3:30h without using inhibitor for methanol dehydrogenase (MDH) enzyme. Sequencing batch process, at the next step, was used to create intermediate lag phase and to increase the stability of microorganisms by forming flocs. The results of this study cleared that the designed system is safe and efficient to scale-up, and it can be considered as a potential alternative method in the production of methanol.

Response of Tisochrysis lutea [Prymnesiophycidae] to aeration conditions in a bench-scale photobioreactor

The effects of superficial gas velocity (Ugr), gas entrance velocity (ν), and bubble size on the growth of Tisochrysis lutea was investigated in 600-mL photobioreactors operated with airlift pumps. Superficial gas velocities, calculated from measured air flow rates, ranging from 7 to 93 mm s−1 were created using a 1.6-mm diameter syringe. We tested the effects of sparger velocity over a range of 2.48 to 73.4 m s−1 and the effects of bubble size by using two styles of air stones and an open glass pipette, which created a bubble sizes in the range of 0.5 to 5 mm. We calculated oxygen mass transfer coefficient, kLa, values for all experimental conditions. Cell growth increased linearly with increased superficial gas velocity and decreased with increased sparger velocity. Results indicated that smaller bubble size leads to some initial cell damage, but after time, the increased gas transfer as reflected by the kLa value produced higher growth than larger bubbles. Two mechanisms were observed to correlate with cell damage in T. lutea: increasing velocity at the sparger tip and bubble bursting at the surface. These results demonstrate a method to test sensitivity of T. lutea to aeration, which is important for the design of airlift systems.

Effect of Biomass Concentration on Oxygen Mass Transfer, Power Consumption, Interfacial Tension and Hydrodynamics in a Multiphase Partitioning Bioreactor

Abstract Several studies have reported that the hydrodynamics are not affected by the biomass in multiphase partitioning bioreactors. This work aims to demonstrate the effect of biomass concentration (0, 1, 3 and 5 g L−1) on the oxygen mass transfer coefficients, the droplet size of the dispersed phase, power consumption and superficial tension in a multiphase partitioning bioreactor (ionic liquid-aqueous-air-biomass system). At a biomass concentration of 5 g L−1, the oxygen mass transfer coefficient (kLa) increased by 55% (249 h−1) compared with the abiotic system (160 h−1). In the multiphasic system, the droplet size (d32) decreased when the biomass concentration was increased, producing an increment in the mass transfer area of the dispersed phase. In addition, the power consumption decreased by 44 % compared to a previous report without biomass. Furthermore, the increment of biomass concentration decreased the superficial tension by up to 15 %. A biomass increment in a multiphase system not also increases product yield, but also enhances the bioconversion process. The results obtained suggest that it is obligatory to consider the effect of biomass concentration on hydrodynamic characterisation, design, scale-up and optimisation for improving the performance of biotechnological processes using multiphase bioreactors.

The Study of Micro-Pressure Inner-Loop Bioreactor Oxygen Mass Transfer Characteristics

The oxygen mass transfer characteristics in a Micro-Pressure Inner-Loop bioreactor (MPR) were studied by clean water oxygenation experiment, the results show that when the aeration adopt by 0.1, 0.2, 0.4, 0.6 m3·h-1, respectively, the oxygen mass transfer coefficient KLa(20) in the reactor increases with the increase of the aeration. KLa(20) shows a good linear correlation with the aeration. The rate is 0.2128 h·m-3·min-1 and the correlation coefficient R=0.993. However, the trend of EO2 increases first and then decreases with the increase of aeration. When the aeration increased to 0.4 m3·h-1, the EO2 reaches the maximum. If aeration increases constantly, EO2 begin to decrease excessive aeration may lead to an increase in energy waste during reactor operation.

Enhancement of bioelectricity generation and algal productivity in microbial carbon-capture cell using low cost coconut shell as membrane separator

Proton exchange membranes (PEMs) are the most prominently used separator in microbial fuel cell (MFC) and microbial carbon capture cell (MCC). This study aims at evaluating the characteristics of coconut shell (CS) to explore its potential as a PEM. The CS exhibited superior water absorption (32%), which can stimulate the proton transmission through water molecules to the cathodic chamber. The proton conductivity of CS separator was comparable to Nafion 117; however, the oxygen mass transfer coefficient of CS separator was lower than Nafion 117, indicating it as superior separator. These separators were used in MCC with Chlorella sorokiniana grown in cathodic chamber. The maximum power density (MPD) and coulombic efficiency (CE) of MCC with CS separator were 3.2 W/m3 and 16.53%, respectively, whereas the MCC with Nafion 117 membrane showed a MPD of 1.8 W/m3 and CE of 8.42%. Although the COD removal efficiency in the anodic chamber of Nafion-MCC (72.14 ± 0.15%) was superior to CS-MCC (65.97 ± 0.83%), the algal specific growth rate at cathode was found better in CS-MCC (2.64 day−1) than Nafion-MCC (2.16 day−1). This study reveals the feasibility of using CS as low cost as well as energy efficient membrane separator for the application in MCC.

Hydrodynamics and oxygen transfer characterization in a net draft tube airlift reactor with water-in-diesel microemulsion

The objective of the present work was to characterize gas holdup (εG), volumetric oxygen mass transfer coefficient (kLa), and specific gas-liquid interfacial area (a) in a water-in-diesel microemulsion (WDME) as a liquid model for aerobic biodesulfurization inside an airlift reactor with a net draft tube (ALR-NDT) when aerated at different rates ranging from 0.05 to 1vvm. For comparison, the hydrodynamics of ALR (with solid draft tube) and bubble column reactor (‘BCR’, with no use of draft tube) were also studied for water, diesel and WDME systems. In all reactors, the εG and kLa values for diesel-based liquids were higher compared to the water system. This indicates the coalescence-inhibiting tendency of petroleum liquids mainly due to the lower surface tension which resulted to a decrease in bubble size distribution (i.e., 0.29–1.90mm for the WDME versus 0.43–14.17mm for water in the ALR-NDT). Although the kLa values in ALR-NDT were maintained between those values obtained in ALR and BCR for all fluids; however, the transition points from homogeneous to heterogeneous regime were shifted to higher aerations in the ALR-NDT. In this regard, empirical correlations were developed by considering the physicochemical properties of the liquid phase and superficial gas velocity.

Multi-chamber single-use bioreactor– A proof of concept prototype

Stirred tank single-use bioreactors have proven their capability to successfully replace their stainless-steel counterparts in the biopharmaceutical industry. To date, however, only a five-fold volume expansion is achievable in a single-use stirred tank bioreactor, which in turn, necessitates intermediate equipment to scale up the culture to production volume. This study introduces a two-chamber single-use bioreactor that is capable of cell culture expansion from 1 to 50L. The prototype is a proof of concept that can help users save costs of purchase and qualification of equipment, reduce factory footprint, and reduce the risk of contamination during culture transfer from one intermediate bag to another. The prototype is made of two chambers of different volumes, interconnected as a single, closed system. The design and construction of the prototype is described in detail and results from the engineering characterization (e.g., mixing time, power input per unit volume, and oxygen mass transfer coefficient) are reported for both chambers. The results are in good agreement with general criteria proposed in literature for bioreactor design and with published data for commercially available bioreactors. Further, the concept is not limited to the two-chamber design presented in this study; additional chambers can be integrated along with different volumes, geometries, mixing, sparging, and heating approaches.

Experimental and CFD physical characterization of animal cell bioreactors: From micro- to production scale

Transfer of mammalian cell culture processes across stirred and aerated bioreactor scales is a delicate task, frequently leading to different conditions across scales. To provide a more rational reasoning behind scale-up of mammalian cell cultures, physical characterization of bioreactors with working volumes of 15 mL, 3 L, 270 L, 5′000 L and 15′000 L was carried out using a combination of computational and experimental methods. Maximum hydrodynamic stress, mixing time and oxygen mass transfer coefficients were experimentally determined for all bioreactor scales. Computational fluid dynamic (CFD) simulations based on Reynolds-averaged Navier‐Stokes equation coupled with bubble size population balance equations were used to determine local as well as average hydrodynamic stresses and mass transfer coefficients. Furthermore, mixing times were determined by simulated tracer experiments. All calculations are well in agreement with experimentally measured values, thereby providing a validation of the CFD simulations. This integrated experimental and modeling methodology represents a valuable tool for a Quality-by-Design approach enabling the transfer of mammalian cell cultures in-between reactor scales, even for geometrically different reactors. Additionally, this study provides a rational framework to transfer an operating space developed at small scale to larger scales.

Experimental and computational studies of oxygen transport in a Taylor-Couette bioreactor

With research and development for almost one century, the Taylor-Couette device is now applied in many practical applications such as reaction, filtration, extraction and bioreactor. We intend to use the Taylor-Couette bioreactor to culture cells that are seeded in a biodegradable porous scaffold. Oxygen concentration is always the most significant constraint in a bioreactor and can limit the cell proliferation rate. It is therefore important to know the mass transfer phenomenon and oxygen transport pattern inside the system. In this study, the equilibrium oxygen concentrations at different Reynolds numbers and operation conditions were measured and the mass transfer coefficients were also calculated. CFD simulation was carried out to compare with the experimental results. Both experimental and simulation results showed that the equilibrium oxygen concentration and mass transfer coefficient increased with Reynolds number. To further improve the mass transfer efficiency, air bubble was introduced to the bottom of the rotating inner cylinder and the vortex center. It was shown that the mass transfer coefficient of oxygen could be significantly increased with the trapped bubble.

Oxygen Transfer in High Solids Loading and Highly Viscous Lignocellulose Hydrolysates

High product concentration in aerobic biorefining fermentation requires high lignocellulose feedstock loading. However, the high solids content and the consequent high viscosity of the lignocellulose hydrolysate severely limit oxygen transfer and thus lead to low aerobic fermentation rate. This study first investigates the experimental measurement and the computational fluid dynamics (CFD)-based simulation of oxygen transfer properties in the high solids loading and highly viscous lignocellulose hydrolysates. The oxygen mass transfer coefficients kLa values vary with various biorefining processing parameters. A minimum threshold kLa value was required for aerobic fermentation of glucose oxidation into gluconic acid. The rheological properties of the slurry were experimentally determined, and a CFD model was established for the design of aerobic fermentation bioreactors. The kLa values between the CFD calculation and the experimental determination were in good agreement for the high solids loading and high...

Optimum spacing between electrodes in an air-cathode single chamber microbial fuel cell with a low-cost polypropylene separator.

The performance of a single chamber microbial fuel cell (MFC) with a low-cost polypropylene separator was investigated at various electrode interspaces in a separator electrode assembly (SEA). The lag period was shortened (3.74-0.17days) and voltage generation was enhanced (0.2-0.5V) as electrode spacing was increased from 0 to 9mm. Power density was increased from 220 to 370 mW/m2 with increased spacing. The highest power density of 488mW/m2 was obtained in polarization analysis with 6mm. The oxygen mass transfer coefficients with 0mm (K o=3.69×10-5cm/s) electrode spacing were 3.8 times higher than with 9mm (K o=0.96×10-5cm/s) spacing. Columbic efficiency (CE) was increased from 5 to 32% due to less oxygen diffusion with increase in electrode spacing, but on contrary the ohmic resistance (R oh) was increased from 2 to 4Ω. In a long-term operation (200days), a gradual decrease in cathode potentials was observed in all electrode spacing as the main limiting factor of stable MFC performance.

Oxygen mass transfer and shear stress effects on Pseudomonas putida BCRC 14365 growth to improve bioreactor design and performance.

In this work, the experimental evidence is presented for two basic issues including oxygen mass transfer and shear analysis on the microorganism containing medium on the most prominent sections of the bioreactor. Computational fluid dynamics (CFD) methodology reproduces shear rate values for specific impeller designs using the commercial code (Fluent 6.2). CFD calculates volumetric mass transfer coefficient based on the Higbie's penetration theory. Four types of impeller are used. The spherical probe is used to measure flow hydrodynamic parameters to obtain shear rate by electro-diffusion (ED) method. The obtained results are validated experimentally and it is shown that a fully axial pattern impeller represents more enhanced results than partially axial and radial. In this regard, experimental results for volumetric oxygen mass transfer coefficient (k l a) confirm CFD predictions by acceptable deviations of 2.65, 8.90, and 9.20 for 0.15, 0.2, and 0.3 VVM, respectively. These results collaboratively indicate that LIGHTNIN-C 200 type operates more efficiently by reflecting the flow to the bottom corner stagnation areas with the minimum tolerable shear and the most velocity distribution uniformity. Furthermore, the values of k l a improve by aeration rate. Conversely, increasing the rotational speed of impeller creates difficulties for cell growth due to the generated harsh shear condition. CFD provide a better understanding of how operational and geometrical variables may be manipulated to achieve a moderate shear rate and acceptable level of mass transfer.

Reaction kinetics of non-catalyzed jet aeration oxidation of magnesium sulfite

Magnesium sulfite oxidation is a key factor influencing the desulfurization efficiency and effluent quality of magnesium desulfurization processes. Non-catalyzed jet aeration is a promising method for the oxidation of magnesium sulfite because of its high gas-liquid mass transfer efficiency. In this work, the reaction kinetics of the jet aeration oxidation of magnesium sulfite were investigated by the two-film theory. The experiments of clean water aeration showed that the oxygen transfer coefficient of jet aeration increased with the liquid flow rate. The results of jet aeration oxidation of magnesium sulfite revealed that the oxidation process could be divided into two stages according to the concentration of magnesium sulfite, i.e., the saturated stage controlled by the oxygen transfer and the unsaturated reaction stage controlled by the oxygen transfer and the sulfite concentration. In the saturated reaction stage, the oxidation rate was found increasing linearly with the increase of the oxygen mass transfer coefficient. The oxidation reaction occurred in the fast reaction regime. In the unsaturated reaction stage, the oxidation reaction rate was 0.62 order in sulfite ion and zero-order in oxygen, whereas the reaction rate constant was found increasing linearly with the oxygen transfer coefficient. The oxidation reaction transited from moderate to slow reaction regime. Results from this work can serve as a useful reference for designing highly efficient jet aeration systems for oxidation of magnesium sulfite.

Modelling of Ozone Mass-Transfer through Non-Porous Membranes for Water Treatment

The mass transfer of ozone and oxygen into water through non-porous membranes was studied using computational fluid dynamics (CFD) modelling and fundamental convection-diffusion theory. Ozone is a gaseous oxidant that is widely applied in drinking water treatment. Membrane contactors are an alternative to conventional gas dispersion methods for injection of ozone gas mixtures into water. Few studies have explored computational approaches for membrane based ozone transport. In this investigation, quantitative concentration profiles across a single polydimethylsiloxane (PDMS) capillary membrane tube with internal gas flow and external liquid flow were obtained, including single mass transfer resistances and overall mass transfer coefficients for ozone and oxygen for varying membrane lengths, thicknesses, and laminar flow liquid side velocities. Both the influence of diffusivity and solubility of gases in the membrane were considered with the applied model. Previous studies have neglected the solubility of gases in the membranes in their analysis of ozone and oxygen gas fluxes. This work shows that the solubility has a significant impact of the overall mass transfer coefficients, in particular for oxygen. The main resistance for ozone was found in the liquid side, while for oxygen it was in the membrane. Mass transfer correlations based on heat transfer analogies revealed Sherwood (Sh) correlations for ozone and oxygen with good agreement to literature data, indicating that the applied computational model returns sensible results. The outcome of this study provides an initial basis for computational predictions of ozone and oxygen mass transfer for different membrane materials, flow conditions and reactor designs.

A mathematical model of aerobic methane oxidation coupled to denitrification

ABSTRACTAerobic methanotrophic bacteria use methane as their only source of energy and carbon. They release organic compounds that can serve as electron donors for co-existing denitrifiers. This interaction between methanotrophs and denitrifiers is known to contribute to nitrogen losses in natural environments and has also been exploited by researchers for denitrification of nitrate-contaminated wastewater. The purpose of this study was to develop a mathematical model describing aerobic methane oxidation coupled to denitrification in suspended-growth reactors. The model considered the activities of three microbial groups: aerobic methanotrophs, facultative methylotrophs, and facultative heterotrophs. The model was tested against data from the scientific literature and used to explore the effects of the oxygen mass transfer coefficient, the solids retention time, and the fraction methane in the feed gas on nitrate removal. The fraction of methane in the feed gas was found to be critical for the nitrate removal rate. A value of about 15% in air was optimal. A lower methane fraction led to excess oxygen, which was detrimental for denitrification. A higher fraction led to oxygen-limitation, which restricted the growth rate of methanotrophs in the reactor.