Volumetric Oxygen Transfer Coefficient Research Articles

Enhancement of Gas Holdup and Oxygen Transfer in Three-Phase Circulating Fluidized-Bed Bioreactors with Swirling Flow

Enhancement of gas holdup and oxygen transfer was investigated in the riser of a three-phase circulating fluidized bed, with a diameter of 0.102 m (ID) and a height of 3.5 m, by means of liquid swirling flow. Effects of gas (0.01–0.07 m/s) and liquid (0.17–0.44 m/s) velocities, fluidized solid particle size (1.0, 1.7, 2.1, 3.0 mm), solid circulation rate (2–8 kg/(m2 s)) and swirling liquid ratio (0–0.5) on the gas holdup and volumetric oxygen transfer coefficient in the riser were examined. The gas holdup and oxygen transfer coefficient could be increased up to 25–30% and 20–25% respectively, by means of liquid swirling flow in the riser. The values of gas holdup and volumetric oxygen transfer coefficients were well correlated in terms of dimensionless groups as well as operation variables within these experimental conditions.

Production of bacterial cellulose by Gluconacetobacter hasenii using a new bioreactor equipped with centrifugal impeller

− In order to improve the bacterial cellulose(BC) production yield, centrifugal and inclined centrifugal impellers were developed. A 6 flat-blade turbine impeller was used as a control system. The flow pattern in the fermenter and volumetric oxygen transfer coefficient(k L a) of these fermentation systems were studied. Fermentations were carried out for the production of BC by G. hansenii PJK in a 2-L jar fermenter equipped with new impellers. Liquid medium was circulated from the bottom, through the cylinder of the impeller and to the wall. The volumetric oxygen transfer coefficients, k L a, of inclined centrifugal and centrifugal impeller systems at 100 rpm were 23 and 15% of the conventional turbine impeller system, respectively. However, the conversion of microbial cells to cellulose non-producing mutant decreased and this results in the increase in BC production at low rotating speed of impellers.

Surfactant Effects on Aeration Performance of Stirred Tank Reactors

AbstractThe effect of surfactants on aeration performance in stirred tank reactors (STR) at high rates of foaming is studied. The volumetric oxygen transfer coefficient (kLa) and foaming activity estimated as foaming height (Hf) were determined. Biotechnology of lipopeptide biosurfactants from aerobic organisms, e.g., Bacillus subtilis were addressed. Using model solutions of known foam‐generating properties, high‐molecular weight surfactin and low‐molecular weight sodium dodecyl sulphate (SDS), as well as impellers of different types, with flat and fluid‐foil blades, clues on the concentration dependence of STR oxygen transfer and foaming as well as options for foam reduction in the presence of biosurfactant were sought. In response to a two‐fold decrease of surface tension by surfactin, kLa values decreased up to 30 % but remained within the range expected for the mixing system in water; the experiments with SDS showing stronger dependence on surfactant concentration and surface tension. Mixing of surfactant media by a standard six‐blade disc turbine (RT) imposed rate limitations on gassing. A low‐shear impeller Narcissus (NS) could be used to avoid bulk foam outflow, while preserving kLa values that remained unchanged. The ‘power per unit volume' correlation of kLa in stirred tanks is tested in the presence of surfactin.

A numerical analysis of effects of vortex breakdown on oxygen transport in a micro-bioreactor

Vortex breakdown effects on oxygen concentration distributions in a micro-bioreactor were investigated by a finite volume model. The bioreactor consists of a cylindrical chamber with a rotating bottom wall. The minimum oxygen concentration and volumetric oxygen transfer coefficient were summarized at different Reynolds numbers, Damkohler numbers as well as bioreactor aspect ratios. It was found that vortex breakdown extends the axis region where oxygen concentration is higher. Also vortex breakdown tends to induce a uniform oxygen concentration distribution in the bioreactor. Thus, the occurrence of vortex breakdown is of benefit to animal cell culture. Compared with that in the bioreactor with a rigid lid, vortex breakdown in the bioreactor with free surface may be better for animal cell culture as the bubble has larger size and may occur apart from the axis.

Determination of the average shear rate in a stirred and aerated tank bioreactor

A method for evaluating the average shear rate ((.)gamma(av)) in a stirred and aerated tank bioreactor has been proposed for non-Newtonian fluids. The volumetric oxygen transfer coefficient (k(L)a) was chosen as the appropriate characteristic parameter to evaluate the average shear rate ((.)gamma(av)). The correlations for the average shear rate as a function of N and rheological properties of the fluid (K and n) were obtained for two airflow rate conditions (phi(air)). The shear rate values estimated by the proposed methodology lay within the range of the values calculated by classical correlations. The proposed correlations were utilized to predict the (.)gamma(av) during the Streptomyces clavuligerus cultivations carried out at 0.5 vvm and four different rotational impeller speeds. The results show that the values of the average shear rate ((.)gamma(av)) varied from 437 to 2,693 s(-1) by increasing with N and flow index (n) and decreasing with the fluid consistency index (K).

Production of carbonyl reductase by Geotrichum candidum in a laboratory scale bioreactor

Fungal fermentation is very complex in nature due to its nonlinear relationship with the time, especially in batch culture. Growth and production of carbonyl reductase by Geotrichum candidum NCIM 980 have been studied in a laboratory scale stirred tank bioreactor at different pH (uncontrolled and controlled), agitation, aeration and dissolved oxygen concentration. The yield of the process has been calculated in terms of glucose consumed. Initial studies showed that fermenter grown cells have more than 15 times higher activity than that of the shake flask grown cells. The medium pH was found to have unspecific but significant influence on the enzyme productivity. However, at controlled pH 5.5 the specific enzyme activity was highest (306 U/mg). Higher agitation had detrimental effect on the cell mass production. Dissolved oxygen concentration was maintained by automatic control of the agitation speed at an aeration rate of 0.6 volume per volume per minute (vvm). Optimization of glucose concentration yielded 21 g/l cell mass with and 9.77 × 10 3 U carbonyl reductase activity/g glucose. Adaptation of different strategies for glucose feeding in the fermenter broth was helpful in increasing the process yield. Feeding of glucose at a continuous rate after 3 h of cultivation yielded 0.97 g cell mass/g glucose corresponding to 29.1 g/l cell mass. Volumetric oxygen transfer coefficient ( K La) increased with the increasing of agitation rate.

Effect of aeration and agitation on the protease production by Staphylococcus aureus mutant RC128 in a stirred tank bioreactor

The modified rotating simplex method has been successfully used to determine the best combination of agitation rate and aeration rate for maximum production of extracellular proteases by Staphylococcus aureus mutant RC128, in a stirred tank bioreactor operated in a discontinuous way. This mutant has shown altered exoprotein production, specially enhanced protease production. Maximum production of proteases (15.28 UP/ml), measured using azocasein as a substrate, was obtained at exponential growth phase when the bioreactor was operated at 300 rpm and at 2 vvm with a volumetric oxygen transfer coefficient (K(L)a) of 175.75 h(-1). These conditions were found to be more suitable for protease production.

Effects of different glycerol feeding strategies on S-adenosyl- l-methionine biosynthesis by P GAP-driven Pichia pastoris overexpressing methionine adenosyltransferase

Methionine adenosyltransferase (MAT) was overexpressed within Pichia pastoris employing the promoter of glyceraldehyde-3-phosphate dehydrogenase gene (P GAP), to biosynthesize S-adenosyl- l-methionine (SAM). Effects of five glycerol feeding tactics on MAT activity were first investigated. Strategies A–C were based on limited feeding correlated with dissolved oxygen (DO) at 50.0%, 25.0% and 0.0%, respectively. For strategies D and E, unlimited supplementation was executed by pulsed feeding mode. Gradual decline (2–0%) (w:v) of the residual glycerol level was shown between any two pulses in strategy D, while a nearly stable content (2%) throughout fed-batch cultivation with strategy E. With shifting strategies A–E in alphabetical order, gradual improvements of MAT activities were achieved, with the maximum of 9.05 U g −1 dried biomass for strategy E, since the specific glycerol consumption rate ( F G) ascended due to the elevated specific oxygen uptake rate ( q O 2 ). The success was ascribed to the enhancement of oxygen transfer rate (OTR), because 2% glycerol improved oxygen saturation content in broth ( C*) and volumetric oxygen transfer coefficient ( k L a). Strategy E also led to the highest values of ATP and biomass besides MAT. Consequently, the highest SAM yield and volumetric level were obtained at 0.058 g g −1 and 9.26 g l −1, respectively.

Oxygen Transfer by Multiple Inclined Plunging Water Jets

There has been a growing interest in the oxygenation by plunging water jets in the last few years due to their inherent advantages, like energy-efficient, low operation cost, etc. Though a lot of work has been reported on the oxygen-transfer by single plunging water jets but very few studies have been carried out using multiple plunging jets. In this paper, volumetric oxygen-transfer coefficient and oxygen-transfer efficiency has been studied experimentally for multiple inclined plunging jets (having jet plunge angle of 0 60 ) in a pool of water for different configurations, in terms of varying number of jets and jet diameters. This research suggests that the volumetric oxygen-transfer coefficient and oxygentransfer efficiency of the multiple inclined plunging jets for air-water system are significantly higher than those of a single vertical as well as inclined plunging jet for same flow area and other similar conditions. The study also reveals that the oxygen-transfer increase with increase in number of multiple jets under similar conditions, which will be most advantageous and energy-efficient in practical situations when large volumes of wastewaters are to be treated. A relationship between volumetric oxygen-transfer coefficient and jet parameters is also proposed. The suggested relationship predicts the volumetric oxygen-transfer coefficient for multiple inclined plunging jet(s) within a scatter of ±15 percent. The relationship will be quite useful in scale-up and in deciding optimum configuration of multiple inclined plunging jet aeration system. Keywords—Multiple inclined plunging jets, jet plunge angle, volumetric oxygen-transfer coefficient, oxygen-transfer efficiency.

Oxygen Transfer in a Three-Phase Circulating Fluidized Bed with Viscous Liquid Medium

Characteristics of oxygen transfer were investigated in the riser of a viscous three-phase circulating fluidized bed, with a diameter of 0.102 m (ID) and a height of 3.5 m. Effects of gas (0.01–0.09 m/s) and liquid (0.12–0.43 m/s) velocities, fluidized solid particle size (1.0, 1.7, 2.1, 3.0 mm), solid circulation rate (2–8 kg/(m2·s)) and liquid viscosity (0.96–38 mPa·s) on the volumetric oxygen transfer coefficient in the riser were examined. The oxygen transfer coefficient was found to increase with increasing gas velocity, particle size and solid circulation rate, while it decreased with increasing viscosity of the continuous liquid medium, and changed very little with the variation of liquid velocity. The oxygen transfer coefficients were well correlated in terms of dimensionless groups as well as operation variables.

An actively mixed mini‐bioreactor for protein production from suspended animal cells

Biopharmaceutical production would benefit from rapid methods to optimize production of therapeutic proteins by screening host cell line/vector combination, culture media, and operational parameters such as timing of induction. Miniaturized bioreactors are an emerging research area aiming at improving the development speed. In this work, a 3 mm thick mini-bioreactor including two 12 mm wide culture chambers connected by a 5 mm wide channel is described. Active mixing is achieved by pressure shuttling between the two chambers. Gas-liquid phase exchange for oxygen and carbon dioxide is realized by molecular diffusion through 50 microm thick polymethylpentene membranes. With this unique design, a velocity difference between the middle area and the side areas at the interfaces of the culture chambers and the connecting channel is created, which enhances the mixing efficiency. The observed mixing time is on the order of 100 s. The combination of high permeability toward oxygen of polymethylpentene membranes and fluid movement during active pressure shuttling enables higher volumetric oxygen transfer coefficients, 5.7 +/- 0.4-14.8 +/- 0.6 h(-1), to be obtained in the mini-bioreactors than the values found in traditional 50 mL spinner flasks, 2.0-2.5 h(-1). Meanwhile, the calculated volume averaged shear stress, in the range of 10(-2)-10(-1) N/m(2), is within the typical tolerable range of animal cells. To demonstrate the applicability of this mini-bioreactor to culture suspended animal cells, the insect cell, Spodoptera frugiperda, is cultured in mini-bioreactors operated under a K(L)a value of 14.8 +/- 0.6 h(-1) and compared to the same cells cultured in 50 mL spinner flasks operated under a K(L)a value of 2.2 h(-1). Sf-21 cells cultured in the mini-bioreactors present comparable length of lag phases and growth rates to their counterparts cultured in 50 mL spinner flasks, but achieve a higher maximum cell density of 5.3 +/- 0.9 x 10(6) cell/mL than the value of 3.4 +/- 0.4 x 10(6) cell/mL obtained by cells cultured in 50 mL spinner flasks. Sf-21 cells infected with SEAP-baculovirus produce a maximum SEAP concentration of 11.3 +/- 0.7 U/mL when cultured in the mini-bioreactor. In contrast, infected Sf-21 cells cultured in 50 mL spinner flasks produce a maximum SEAP concentration of 7.4 +/- 0.9 U/mL and onset of production is delayed from 18 h in minibioreactor to 40 h in spinner flasks.

Air-Water Oxygen Transfer with Multiple Plunging Jets

Abstract Despite numerous works reporting on oxygen transfer by plunging jets, few studies have been carried out on multiple plunging jets. In this paper, the volumetric oxygen-transfer coefficient and oxygen-transfer efficiency of multiple plunging jets in a pool of water for different configurations in terms of varying numbers of jets and jet diameters were studied experimentally. This research suggests that the volumetric oxygen-transfer coefficient and oxygen-transfer efficiency of the multiple plunging jets for air/water systems were significantly higher than those of a single plunging jet for same flow area and other similar conditions. A relationship between the volumetric oxygen-transfer coefficient and jet parameters is also proposed. The suggested relationship predicted the volumetric oxygen-transfer coefficient for single and multiple plunging jet(s) within a scatter of ±15%.

Average shear rate for non-Newtonian fluids in a concentric-tube airlift bioreactor

In the present study, a simple methodology for evaluating the average shear rate ( γ ˙ av ) in an internal concentric-tube airlift reactor has been developed for non-Newtonian systems. The volumetric oxygen transfer coefficient ( k L a) was chosen as the appropriate characteristic parameter to evaluate the average shear rate ( γ ˙ av ) because the oxygen transfer occurs through the interfacial area of the air bubbles distributed evenly throughout the bioreactor. The average shear rate ( γ ˙ av ) values of up to 9300 s −1 were estimated as a function of the gas velocity in the riser (0.0094 ≤ U GR ≤ 0.0943 m s −1), of the rheological parameters of the fluid (0.180 ≤ K ≤ 1.833 Pa s n and 0.234 ≤ n ≤ 0.461), and of the volumetric oxygen transfer coefficient (0.0056 ≤ k L a ≤ 0.0609 s −1). Profiles of the γ ˙ av as a function of the gas velocity in the riser ( U GR) displayed different behaviors from those of the literature since γ ˙ av increased up to a maximum value and then decreased with an increase in the U GR. The shear rate estimated by the proposed methodology lay within the range of the correlation values in the literature. Unlike other correlations in the literature, the average shear rate in the present study ( γ ˙ av ) is estimated considering the rheological parameters of the fluid, the volumetric oxygen transfer coefficient ( k L a), and the mass transfer parameter, which is a function of the operating conditions and the geometry of the bioreactor.

Production of Medium-Chain-Length Poly(3-hydroxyalkanoates) from Crude Fatty Acids Mixture by Pseudomonas putida

Microbial production of medium-chain-length poly(3-hydroxyalkanoates), PHA MCL from crude fatty acids mixture was investigated. With ammonium as the growth limiting substrate, fatty acids mixture from saponified palm kernel oil (SPKO) supports good growth and PHA MCL production of Pseudomonas putida PGA1. Growth of this microorganism on ammonium exhibited substrate inhibition kinetics which can be described using Andrews model with the substrate inhibition constant, K i = 1.2 g L −1. Concentration of SPKO in the aqueous medium should be at 10 g L −1 or less, as higher concentrations can significantly reduced the volumetric oxygen transfer coefficient (K L a), biomass growth and PHA MCL production. Uptake of SPKO by the organism follows a zero-order kinetics, indicating a mass transfer limitation of the free fatty acids by the P. putida PGA1 cells. In batch and fed-batch fermentations, PHA MCL accumulation is encouraged under ammonium-limited condition with SPKO as the sole carbon and energy source. The amount of PHA MCL accumulated and its specific production rate, q PHA were influenced by the residual ammonium concentration level in the culture medium. It was observed that in both fermentation modes, when the residual ammonium becomes exhausted (<0.05 g L −1), the PHA MCL accumulation and q PHA were significantly reduced. However, this effect can be reversed by feeding low amount of ammonium to the culture, resulting in significantly improved PHA MCL yield and productivity. It is concluded that the feeding of residual ammonium concentration in the culture medium during the PHA MCL accumulation has a positive effect on sustaining the PHA MCL biosynthetic capability of the organism.

Effects of floating contactors on oxygen transfer and hydrodynamics in a bubble column

This study investigates the adoption of floating contactors to promote the rate of oxygen transfer from non-uniform air bubbles to liquid in a bubble column with continuous operation. The volumetric oxygen transfer coefficient and axial dispersion coefficient of a liquid phase have been analyzed based on the axial dispersion model. Attention was focused on the effects of the volume fraction of the floating contactors on the volumetric oxygen transfer coefficient, axial dispersion coefficient of a liquid phase, and gas phase hold-up in the bubble column. The results have shown that the volumetric oxygen transfer coefficient and gas phase hold-up can increase by up to 25% and 13%, respectively, while the axial dispersion coefficient of a liquid phase decreases by up to 30% by adding floating contactors in the column.

Submerged monoxenic culture of the entomopathogenic nematode Steinernema carpocapsae in an internal‐loop airlift bioreactor using two configurations of the inner tube

This article reports the submerged culture of the entomopathogenic nematode Steinernema carpocapsae and its symbiotic bacterium, Xenorhabdus nematophila, within an internal-loop airlift bioreactor. Two configurations of the inner cylinder were tested: a standard draft tube (SDT) and a static mixer (SM), as well as two production media: MP1 (500 mL/L whey, among other ingredients) and MP2 (82 mL/L agave-juice from Agave spp., among other ingredients). Three fermentations were carried out: F1 --> SDT-MP1, F2 --> SM-MP1 and F3 --> SM-MP2. The operating conditions were expressed on the basis of dimensionless Reynolds number (Re) and volumetric oxygen transfer coefficient (k(L)a), both of them determined on riser and downcomer sections within the bioreactor. The experiments began with fewer than 1,000 infective juvenile nematode stages (IJ) per mL and at t = 20 d, they achieved (nematodes/mL-%IJ) 222,000-87%, 62,200-23% and 114,600-80%, within F1, F2 and F3 experiments, respectively. Nonetheless, the achieved maximum nematode biomass concentrations (g/L) were F1 --> 408, F2 --> 557 and F3 --> 613, and occurred at t = 16, 10 and 12 d, respectively. The fermentation operating conditions involved 0.042 (-) < Re < 647 (-) and 2.8 x 10(-4) s(-1) < k(L)a < 0.0447 s(-1), as functions of 0.004 m/s < superficial gas velocity (within the riser) < 0.079 m/s, 0.001 m/s < mean downcomer velocity < 0.014 m/s, and culture broth rheological properties which evolved from nearly the Newtonian behaviour to the pseudoplastic one. The maximum IJ concentration was achieved within F1 experiment (193,406 IJ/mL). Also, fermentation conditions involving higher riser-Re and lower downcomer-Re as well as higher nutriment concentrations in culture medium, promote higher nematode biomass concentrations but lower %IJ, maybe as a result of better conditions for the nematode population development.

Long term performance of MBR for biological nitrogen removal from synthetic municipal wastewater

This study monitors the long term performance of membrane bioreactor (MBR) for the treatment of synthetic municipal wastewater at solid retention time (SRT) of 40 and 20 d with particular emphasis on simultaneous nitrification–denitrification (SND). SND was greatly influenced by the operating dissolved oxygen (DO). It was found that at an SRT of 20 d, nitrogen removal through assimilation into biomass increases as a result of higher biomass yield. The profile of soluble microbial products (SMP) conformed to a cyclical pattern in the MBR with respect to SRT. Decrease in SRT from 40 to 20 d resulted in doubling of accumulated SMP concentration (to 56 mg l −1) in the MBR. This however, was accompanied by a simultaneous drop in percentage of SMP with MW > 100 kD, from 42.4% to 33%. Also, the sludge filterability decreased by 24-folds despite a decrease in the biomass concentration, following the above reduction in SRT. It was found that the volumetric oxygen transfer coefficient ( K l a) was a function of biomass concentration in MBR with the ratio of the oxygen transfer coefficient in mixed liquor to that of clean water ( α) to be 0.2–0.5.

Production of Medium-Chain-Length Poly(3-Hydroxyalkanoates) from Saponified Palm Kernel Oil by Pseudomonas putida: Kinetics of Batch and Fed-Batch Fermentations

The kinetics of medium-chain-length poly(3-hydroxyalkanoates), PHAMCL production by Pseudomonas putida PGA1 in batch and fed-batch fermentations were studied. With saponified palm kernel oil (SPKO) supplying the free fatty acids mixture as the sole carbon and energy source, PHAMCL accumulation is encouraged under ammonium-limited condition, which is a nitrogen stress environment. The amount of PHAMCL accumulated and its specific production rate, qPHA were influenced by the residual ammonium concentration level in the culture medium. It was observed that in both fermentation modes, when the residual ammonium was exhausted (< 0.05 gL-1), the PHAMCL accumulation (11.9) and qPHA (0.0062 h-1) were significantly reduced. However, this effect can be reversed by feeding low amount of ammonium to the culture, resulting in significantly improved PHAMCL yield (71.4) and specific productivity (0.6 h-1). It is concluded that the feeding of low ammonium concentration to the culture medium during the PHAMCL accumulation has a positive effect on sustaining the PHAMCL biosynthetic capability of the organism. It was also found that increasing SPKO concentration in the medium significantly reduced (up to 50) the volumetric oxygen transfer coefficient (KLa) of the fermentation system.

A 3D analysis of oxygen transfer in a low-cost micro-bioreactor for animal cell suspension culture

A 3D numerical model was developed to study the flow field and oxygen transport in a micro-bioreactor with a rotating magnetic bar on the bottom to mix the culture medium. The Reynolds number ( Re) was kept in the range of 100–716 to ensure laminar environment for animal cell culture. The volumetric oxygen transfer coefficient ( k L a) was determined from the oxygen concentration distribution. It was found that the effect of the cell consumption on k L a could be negligible. A correlation was proposed to predict the liquid-phase oxygen transfer coefficient ( k Lm) as a function of Re. The overall oxygen transfer coefficient ( k L) was obtained by the two-resistance model. Another correlation, within an error of 15%, was proposed to estimate the minimum oxygen concentration to avoid cell hypoxia. By combination of the correlations, the maximum cell density, which the present micro-bioreactor could support, was predicted to be in the order of 10 12 cells m −3. The results are comparable with typical values reported for animal cell growth in mechanically stirred bioreactors.

Kinetics, Mass Transfer and Hydrodynamics in a Packed Bed Aerobic Reactor Fed with Anaerobically Treated Domestic Sewage

This study presents an assessment of the kinetic, mass transfer and hydrodynamic parameters of a pilot-scale fixed bed reactor containing immobilized biomass in polyurethane matrices and fed with the effluent of a horizontal-flow fixed bed anaerobic reactor, which was used to treat domestic sewage. It was found that the liquid-solid and intra-particle mass transfer resistances significantly affected the overall oxygen consumption rate and that mechanical agitation could minimize such resistances. The volumetric oxygen transfer coefficient (kLa) values for superficial air velocities between 8.4 cm min&minus1 and 57.0 cm min&minus1 varied from 20.8 h&minus1 to 58.8 h&minus1 for tap water, and 16.8 h&minus1 to 53.0 h&minus1 for the anaerobic pre-treated effluent. The intrinsic oxygen uptake rate was estimated to be 19.9 mgO2 gVSS&minus1 h&minus1. A first-order kinetic model with residual concentration was considered to adequately represent the COD removal rate, whereas nitrogen conversion was considered to be well represented by a model of pseudo-first-order reaction in series. It was also found that the ammonium conversion to nitrite was the limiting step of the overall nitrogen conversion rate. The hydrodynamic behavior of the reactor was represented by three to four completely mixed reactors in series.