Volumetric Oxygen Transfer Rate Research Articles

Effect of Gas Sources on the Oxygen Transfer Efficiency Produced by Fine Bubbles Generator

Fine bubbles (micro to nanometer-sized) have rapidly gained popularity in academia and industry due to their unique properties, such as their high surface area, stability, and longevity. In this study, the performance of oxygen transfer rate efficiency in fine bubbles with high purity oxygen and atmospheric air was analyzed. In this study, the developed fine bubbles generator with power requirement 300 watt was used to evaluate the production of fine bubbles and oxygen transfer efficiency at two type gas sources i.e., ambient air and high-purity oxygen in the small bench aqueous media (5 L water tank). The fine bubbles generator was set up at the pressure in 50 psi and gas flow rate at 0.3 L/min to produce fine bubbles in water medium. The effect of water recirculation process in the bubbles production was measured using particles size analyzer (PSA), zeta potential and dissolved oxygen (DO) meter to measure temperature and dissolved oxygen on the water. Dissolved Oxygen (DO) measurement shows the saturation value of oxygen concentration in water, for high purity oxygen is 30 mg/L higher than air which has a value of 8.64 mg/L. This causes the efficiency of gas transfer in high-purity oxygen to reach 72.09% higher than ambient air at 35.39%. The particle size distribution shows that the mean size of bubbles after 10 minutes recirculation was 465.5 nm and 599.9 nm correspondingly for ambient air and oxygen gas source. High purity oxygen also affect to the zeta potential value tends to be more negative than in ambient air. The type of high-purity oxygen gas can increase the efficiency of the oxygen transfer rate so that the gas containing high-purity oxygen increases the volumetric oxygen transfer rate coefficient which is 2 times higher than using ambient air.

Computational fluid dynamics analysis of mixing and gas-liquid mass transfer in wave bag bioreactor.

Single use bioreactors provide an attractive alternative to traditional deep-tank stainless steel bioreactors in process development and more recently manufacturing process. Wave bag bioreactors, in particular, have shown potential applications for cultivation of shear sensitive human and animal cells. However, the lack of knowledge about the complex fluid flow environment prevailing in wave bag bioreactors has so far hampered the development of a scientific rationale for their scale up. In this study, we use computational fluid dynamics (CFD) to investigate the details of the flow field in a 20-L wave bag bioreactor as a function of rocking angle and rocking speed. The results are presented in terms of local and mean velocities, mixing, and energy dissipation rates, which are used to create a process engineering framework for the scale-up of wave bag bioreactors. Proof-of-concept analysis of mixing and fluid flow in the 20-L wave bag bioreactor demonstrates the applicability of the CFD methodology and the temporal and spatial energy dissipation rates integrated and averaged over the liquid volume in the bag provide the means to correlate experimental volumetric oxygen transfer rates (kL a) data with power per unit volume. This correlation could be used as a rule of thumb for scaling up and down the wave bag bioreactors.

Oxygen transfer dynamics and nitrification in a novel rotational sponge reactor

The nitrification process demands higher oxygen supply, which is fulfilled through external aeration in wastewater treatment. To perform nitrification without external aeration, this study developed a novel rotating sponge (RS) reactor and estimated its oxygen transfer capability. The reactor obtained an oxygen transfer coefficient (KLa) value of over 100d−1 at 40 rounds per hour (rph), which is one-eighth of the rotational speed of conventional rotational biological contactors. Within 53days of operation, reactor achieved 97% nitrification efficiency with an effluent NH4+-N concentration of 1mgL−1. On the other hand, the volumetric oxygen transfer rate in the reactor was 245mg-O2L−1d−1 at 10rph during the experimental period. However, the average volumetric oxygen consumption rate during nitrification was 187mg-O2L−1d−1, which was below the oxygen transfer rate. Microbial community analysis revealed high relative abundance of bacteria such as Nitrosomonas, Nitrospira, and Nitrobacter in the RS reactor, which contributed to nitrification.

Oxygen transfer in a pressurized airlift bioreactor.

Airlift bioreactors (ALBs) offer advantages over conventional systems, such as simplicity of construction, reduced risk of contamination, and efficient gas-liquid dispersion with low power consumption. ALBs are usually operated under atmospheric pressure. However, in bioprocesses with high oxygen demand, such as high cell density cultures, oxygen limitation may occur even when operating with high superficial gas velocity and air enriched with oxygen. One way of overcoming this drawback is to pressurize the reactor. In this configuration, it is important to assess the influence of bioreactor internal pressure on the gas hold-up, volumetric oxygen transfer coefficient (k(L)a), and volumetric oxygen transfer rate (OTR). Experiments were carried out in a concentric-tube airlift bioreactor with a 5 dm(3) working volume, equipped with a system for automatic monitoring and control of the pressure, temperature, and inlet gas flow rate. The results showed that, in disagreement with previous published results for bubble column and external loop airlift reactors, overpressure did not significantly affect k(L)a within the studied ranges of pressure (0.1-0.4 MPa) and superficial gas velocity in the riser (0.032-0.065 m s(-1)). Nevertheless, a positive effect on OTR was observed: it increased up to 5.4 times, surpassing by 2.3 times the oxygen transfer in a 4 dm(3) stirred tank reactor operated under standard cultivation conditions. These results contribute to the development of non-conventional reactors, especially pneumatic bioreactors operated using novel strategies for oxygen control.

Innentitelbild Chem. Ing. Tech. 1‐2/2013

AbstractCELL‐tainer©: the disposable bag bioreactor suitable for microbial fermentationDisposable bioreactors have gained an increasing importance in recent years in the pharmaceutical production. Rocking‐mixed reactors were among the first systems which were applied. In contrast to stirred tank reactors, rocking‐mixed bioreactors are characterized by low shear forces, while the gas exchange is realized by the large gas‐liquid interface. The CELL‐tainer© disposable bioreactors are characterized by distinctly higher volumetric oxygen transfer rates of 300 h–1, achieved by a two‐dimensional rocking direction. By applying nutrient‐limiting fed‐batch cultivations, in which the oxygen consumption of a culture is controlled, bacteria can be cultivated in these reactors. The picture shows two CELL‐tainer reactors in which a successful scale‐up of an Escherichia coli fed‐batch cultivation from the 12‐L to the 120‐L scale was performed and a final dry biomass concentration of 45 g L–1 (OD600 = 140) was obtained.S. Junne*, T. Solymosi, N. Oosterhuis, P. Neubauer, Chem. Ing. Tech. 2013, 85 (1 – 2), 57 – 66.DOI: 10.1002/cite.201200149

Aerobic biodegradation of a mixture of sulfonated azo dyes by a bacterial consortium immobilized in a two‐stage sparged packed‐bed biofilm reactor

AbstractThe biodegradation of the sulfonated azo dyes, Acid Orange 7 (AO7) and Acid Red 88 (AR88), by a bacterial consortium isolated from water and soil samples obtained from sites receiving discharges from textile industries, was evaluated. For a better removal of azo dyes and their biodegradation byproducts, an aerobically operated two‐stage rectangular packed‐bed biofilm reactor (2S‐RPBR) was constructed. Because the consortium's metabolic activity is affected by oxygen, the effect of the interstitial air flow rate QGI on 2S‐RPBR's zonal values of the oxygen mass transfer coefficient kLa was estimated. In the operational conditions probed in the bioreactor, the kLa values varied from 3 to 60 h−1, which roughly correspond to volumetric oxygen transfer rates, dcL/dt, ranging from 20 to 375 mg O2 L−1h−1. Complete biodegradation of azo dyes was attained at loading rates BV,AZ up to 40 mg L−1d−1. At higher BV,AZ values (80 mg L−1 d−1), dye decolorization and biodegradation of the intermediaries 4‐amino‐naphthalenesulphonic acid (4‐ANS) and 1‐amino‐2‐naphthol (1‐A2N) was almost complete. However, a diminution in COD and TOC removal efficiencies was observed in correspondence to the 4‐aminobenzenesulfonic acid (4‐ABS) accumulation in the bioreactor. Although the oxygen transport rate improved the azo dye mineralization, the results suggest that the removal efficiency of azo dyes was affected by biofilm detachment at relatively high QGI and BV,AZ values. After 225 days of continuous operation of the 2S‐RFBR, eight bacterial strains were isolated from the biofilm attached to the porous support. The identified genera were: Arthrobacter, Variovorax, Agrococcus, Sphingomonas, Sphingopyxis, Methylobacterium, Mesorhizobium, and Microbacterium.

Fungal Bioremediation of Phenolic Wastewaters in an Airlift Reactor

Of the various types of industry-generated effluents, those containing organic pollutants such as phenols are generally difficult to remediate. There is a need to develop new technologies that emphasize the destruction of these pollutants rather than their disposal. In this work the white rot fungus, Trametes pubescens, was demonstrated to be an effective bioremediation agent for the treatment of phenolic wastewaters. An airlift loop reactor was optimized, in terms of volumetric oxygen transfer rate (K(L)a = 0.45 s(-1)), to provide an environment suited to rapid growth of T.pubescens (mu = 0.25 day(-1)) and a particularly efficient growth yield on glucose of 0.87 g biomass.g glucose(-1). The phenolic effluent was shown to be a paramorphogen, influencing fungal pellet morphology in the reactor, as well as increasing laccase enzyme activity by a factor of 5 over the control, to a maximum of 11.8 U.mL(-1). This increased activity was aided by the feeding of nonrepressing amounts (0.5 g.L(-1)) of glucose to the reactor culture. To our knowledge the degradation results represent the highest rate of removal (0.033 g phenol.g biomass(-1).day(-1)) of phenolic compounds from water reported for white rot fungi.

Enhanced treatment of practical textile wastewater by microbubble ozonation

In this paper, microbubble technology was employed to increase the mass transfer rate of ozone and enhance the ozone oxidation of practical textile wastewater. Experiments were performed using a microbubble generator and a bubble contactor, which is commonly used in ozonation system, for comparison. The microbubble generator produced a milky and high intensity microbubble solution, which could reach a higher oxygen transfer rate at a lower input gas flow rate. A volumetric oxygen transfer rate (VOTR) of 0.086–0.413 kg/m 3 h and a total mass transfer coefficient of 0.1072–0.4859 min −1 were obtained at airflow rates of 0.02–1.5 dm 3/min. During the ozonation of practical textile wastewater by using the microbubble system, the input ozone could be almost completely utilized, and the rate of decolorization and organic reduction were much faster than those of the bubble contactor. For the practical textile wastewater tested, the time required for 80% removal of color was about 140 and 280 min by ozone microbubble and conventional bubbles, respectively. The chemical oxygen demand (COD) removal efficiency in the microbubble system was higher by 20%. The results revealed that in addition to the enhancement of the mass transfer of ozone, microbubbles could improve the oxidation of actual textile wastewater.

Oxygen Transfer Rate in a Coarse-Bubble Diffused Aeration System

To improve the performance of a diffused aeration system, a series of aeration studies using various diffusers was initiated. At this stage, 35 unsteady-state reaeration test runs in a 1500-L aeration tank with coarse-bubble diffusers have been performed under varying diffused airflow rates (3.04−8.34 m3/h), water temperatures (17.7−34.7 °C), and water depths (0.6−1.8m). The reaeration data were analyzed by the traditional ASCE model and a two-zone model. The experimental results show that the volumetric mass-transfer coefficients of the ASCE model and of the surface reaeration zone increase with the airflow rate and temperature, but decrease with the water depth. The volumetric mass-transfer coefficient of the gas-bubble zone also increases with the airflow rate and water temperature, but is independent of the water depth. The saturation DO concentrations and the volumetric oxygen transfer rates under varying aeration conditions can be predicted by the two-zone model satisfactorily.

Process-engineering characterization of small-scale bubble columns for microbial process development

Volumetric oxygen transfer rates and power inputs were estimated by a model of the formation of primary gas bubbles at the static sparger (sinter plate) of small-scale bubble columns and a common mass-transfer correlation for bubbles rising in a non-coalescent Newtonian electrolyte solution of low viscosity. Estimations were used to assess the dimensioning and possibilities of small-scale bubble column application with an height/diameter ratio of about 1. Estimations of volumetric oxygen transfer rates (<0.16 s–1) and power inputs (<100 W m–3) with a mean pore diameter of the static sparger of 13 µm were confirmed as function of the superficial air velocity (<0.6 cm s–1) by measurements using an Escherichia coli fermentation medium. Small-scale bubble columns are thus to be classified between shaking flasks and stirred-tank reactors with respect to the oxygen transfer rate, but the maximum volumetric power input is more than one magnitude below the power input in shaking flasks, which is of the same order of magnitude as in stirred-tank reactors. A small-scale bubble columns system was developed for microbial process development, which is characterized by handling in analogy to shaking flasks, high oxygen transfer rates and simultaneous operation of up to 16 small-scale reactors with individual gas supply in an incubation chamber.

Oxygen transfer in agitated silica and pyrite slurries

Oxygen transfer measurements in agitated mineral slurries were carried out in a 671 laboratory tank. Two impellers (a Rushton turbine and a Lightnin A315) and two types of solid particles (silica, d 50=13 μm, and pyrite, d 50=14 μm) were investigated. Next to the volumetric oxygen transfer rate k La local bubble sizes, the overall gas hold-up in the tank, and the power input were measured. The silica and pyrite slurries behaved remarkably different with respect to the oxygen transfer as a function of the solids fraction. The pyrite particles increase ka, whereas silica impairs oxygen transfer. The bubble size measurements indicate that the increased k La in pyrite slurries is related to an increased interfacial area in the tank.

Oxygen transfer and aeration efficiency - influence of diffuser submergence, diffuser density, and blower type

The main factors of fine bubble aeration systems in uniform arrangement in clean water are the air flow rate, the depth of submergence of the diffusers, and the diffuser density. While the influence of the air flow rate on the oxygen transfer parameters is known, knowledge of the influence of the depth of submergence and the diffuser density on the specific oxygen transfer efficiency SOTE [%/m] and on the specific oxygen absorption SOA [g/m3·m at STP] is very limited. Both parameters are of great importance in dimensioning fine bubble aeration systems. Therefore, a literature review was conducted to show the influence of the diffuser submergence and density and the type of blower on oxygen transfer and aeration efficiency. The main review results are, that higher values of specific oxygen absorption can be obtained at higher diffuser density; secondly, the volumetric oxygen transfer rate VOTR [g/m3·h] is higher with increasing depth of submergence at the same air flow rate. Also it can be stated that with greater depth of submergence the specific oxygen absorption [g/m3·m at STP] is reduced. Dependent on the air flow rate and the pressure head, the energy consumption [Wh/m3·m at STP] of the blowers used in wastewater treatment plants is different. For example, the energy consumption varies from 4.3 [Wh/m3·m at STP] (positive displacement blower) to 3.0 [Wh/m3·m at STP] (turbo-compressors) at a pressure of 10 m and an air flow rate of 5,000 m3/h at STP. From the results of the literature review the following conclusions can be drawn: (1) High specific oxygen absorption values (SOA) [g/m3·m at STP] can be achieved applying shallow tanks, high diffuser densities and low specific air flow rates; (2) High aeration efficiencies (AE) [kg/kWh] can be obtained by applying high volumetric oxygen transfer rates and adequate selection of the blowers used at the wastewater treatment plants.

Oxygen transfer and aeration efficiency — Influence of diffuser submergence, diffuser density, and blower type

The main factors of fine bubble aeration systems in uniform arrangement in clean water are the air flow rate, the depth of submergence of the diffusers, and the diffuser density. While the influence of the air flow rate on the oxygen transfer parameters is known, knowledge of the influence of the depth of submergence and the diffuser density on the specific oxygen transfer efficiency SOTE [%/m] and on the specific oxygen absorption SOA [g/m3·m at STP] is very limited. Both parameters are of great importance in dimensioning fine bubble aeration systems. Therefore, a literature review was conducted to show the influence of the diffuser submergence and density and the type of blower on oxygen transfer and aeration efficiency. The main review results are, that higher values of specific oxygen absorption can be obtained at higher diffuser density; secondly, the volumetric oxygen transfer rate VOTR [g/m3·h] is higher with increasing depth of submergence at the same air flow rate. Also it can be stated that with greater depth of submergence the specific oxygen absorption [g/m3·m at STP] is reduced. Dependent on the air flow rate and the pressure head, the energy consumption [Wh/m3·m at STP] of the blowers used in wastewater treatment plants is different For example, the energy consumption varies from 4.3 [Wh/m3·m at STP] (positive displacement blower) to 3.0 [Wh/m3·m at STP] (turbo-compressors) at a pressure of 10 m and an air flow rate of 5,000 m3/h at STP.From the results of the literature review the following conclusions can be drawn: (1) High specific oxygen absorption values (SOA) [g/m3·m at STP] can be achieved applying shallow tanks, high diffuser densities and low specific air flow rates; (2) High aeration efficiencies (AE) [kg/kWh] can be obtained by applying high volumetric oxygen transfer rates and adequate selection of the blowers used at the wastewater treatment plants.

Aeration-controlled formation of acetic acid in heterolactic fermentations

Controlled aeration ofLeuconostoc mesenteroides was studied as a possible mechanism for control of the formation of acetic acid a metabolite of major influence on the taste of lactic fermented foods. Fermentations were carried out in small scale in a medium in which growth was limited by the buffer capacity only. Ethanol and acetic acid formed during the fermentation were analyzed by rapid head space gas chromatography, and the ratio of the molar concentrations of these two volatiles quantitatively predicted the balance between the formation of acetic acid and lactic acid. The oxygen concentration during the fermentations decreased rapidly to zero, meaning that oxygen transfer was limited by the volumetric oxygen transfer rate,k1aC*. A linear correlation between k1aC* and the quantity of acetic acid produced was established, and it is suggested that such oxygenated heterolactic fermentation processes should be analyzed as fed-batch fermentations with oxygen as the limiting substrate. Addition of fructose in limited amounts leads to the formation of one half mole of acetic acid for each mole fructose, thus offering an alternative mechanism for controlling acetic acid formation.

The miniloop: A small‐scale air‐lift microbial culture vessel and photobiological reactor

AbstractThe miniloop culture vessel provides a simple means of obtaining high oxygen transfer rates in a small scale (10 cm3) reactor. The reactor contains no moving parts. The volumetric oxygen transfer rate (measured by Cu2+ catalysed sulphite oxidation) exceeded 400 h−1. The high surface: volume ratio (12 cm−1) permitted photosynthetic algal cultures with biomass densities over 35 g dm−3 in chemostat steady‐states.

Hydrodynamic behaviour and oxygen transfer rate in a pilot plant fermenter: I. Influence of viscosity

AbstractThe effects of varying impeller speed, aeration rate and viscosity on mixing time, power consumption and oxygen transfer rate were studied in the pilot plant fermenter. The rheological behaviour of erythromycin fermentation broth was simulated by colloidal starch solutions at apparent viscosities of 0.02–0.20 Pa/s. The volumetric oxygen transfer rate coefficient was determined by the sulphite and static method. The experimental results showed that at low viscosities, up to of 0.02 Pa/s, the suitable range of impeller speed is 250–300 min−1 at aeration rate 0.6–0.8 VVM from the point of view of power input (2.6–2.8 kW/m3) and sufficient coefficient KLa (160–200 h−1). At viscosities higher than 0.02 Pa/s (with pseudoplastical character) the suitable range of impeller speed is 300–350 min−1 at the same aeration rate. Then the power input for mixing is 3.0–3.5 kW/m3 and the coefficient KLa ∼ 50 h−1.

Hydrodynamic behaviour and oxygen transfer rate in a pilot plant fermenter. I. Influence of viscosity

AbstractThe effects of varying impeller speed, aeration rate and viscosity on mixing time, power consumption and oxygen transfer rate were studied in the pilot plant fermenter. The rheological behaviour of erythromycin fermentation broth was simulated by colloidal starch solutions at apparent viscosities of 0.02–0.20 Pa/s. The volumetric oxygen transfer rate coefficient was determined by the sulphite and static method. The experimental results showed that at low viscosities, up to of 0.02 Pa/s, the suitable range of impeller speed is 250–300 min−1 at aeration rate 0.6–0.8 VVM from the point of view of power input (2.6–2.8 kW/m3) and sufficient coefficient KLa (160–200 h−1). At viscosities higher than 0.02 Pa/s (with pseudoplastical character) the suitable range of impeller speed is 300–350 min−1 at the same aeration rate. Then the power input for mixing is 3.0–3.5 kW/m3 and the coefficient KLa ∼ 50 h−1.

Batch kinetics and oxygen consumption of Candida lipolytica 4-1 on n-alkanes.

Detailed batch kinetics ofCandida lipolytica 4-1 onn-hexadecane for varying dispersed phase volume from 0.5 to 5% v/v is presented. All batch growth curves exhibited a linear growth region, indicating a substrate uptake limit. System productivities derived from the linear region were correlated to the dispersed phase volume. The correlation coefficient was identical with that obtained on gas oil. This implies that a correlation coefficient of interfacial area to the dispersed phase volume is identical for both systems. Dissolved oxygen profile and uptake of oxygen from gas phase were also measured. The oxygen uptake rate, volumetric oxygen transfer rate and oxygen demand (requirement) were calculated by means of the balance method. Under limiting dissolved oxygen concentration the maximal oxygen transfer of the fermenter was assessed.

On the crystal size intensity function and interpreting population density data from crystallizers

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