Volumetric Mass Transfer Coefficient kLa Research Articles

Effect of Oxygen Supply on Surfactin Production and Sporulation in Submerged Culture of Bacillus subtilis Y9

Fermentation parameters for surfactin production and sporulation in a submerged culture of Bacillus subtilis Y9 with various oxygen transfer rates in 5 L jar fermenters were investigated. The oxygen-uptake rate (OUR) was positively correlated with volumetric surfactin productivity. When OUR value increased from 0 to 250 s−1, productivity increased up to 45 mg/L·h; however, no further increase was observed at OUR values above 255 s−1. The volumetric mass transfer coefficient KLa increased with increasing agitation speed. However, a reduction in surfactin production was observed at the highest agitation speed of 500 rpm. Productivity sharply decreased after spore appearance, and remained low until the end of the culture. A mesh-type sparger was installed to generate microsized air bubbles. When the system was operated at 400 rpm with the mesh-type sparger, KLa was higher than that at 500 rpm with an original sparger. Under agitation at 400 rpm with the mesh-type sparger, productivity was maintained above 42.3 mg/L·h until 24 h, resulting in the highest surfactin concentration of 875 mg/L. Thus, a mesh-type sparger promotes KLa, leading to an increase in productivity.

Gas to liquid mass transfer in mixing system with application of rotating magnetic field

This study reports a new multiphase device, the mixer equipped with the rotating magnetic field (RMF) generator, which shows high rates of gas-liquid mass transfer in comparison to a convectional mixer with impeller. The volumetric gas-liquid mass transfer coefficient kLa in the tested apparatus with application of the RMF increases with increasing magnetic field and superficial gas velocity. It is shown that the mass transfer process under the RMF action has significantly higher values of the kLa coefficient than the conventional Rushton turbine or the synergistic effect of the rotational Rushton turbine and the RMF generator. The empirical relationships between this coefficient and the operational parameters obtained in this work can provide helpful guidance for design and operation of set-up equipped with the RMF or the mechanical mixer supported by RMF.

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.

Controlling microbubbles in alcohol solutions by using a multi‐channel ceramic membrane distributor

AbstractBACKGROUNDMicrobubbles are gaining more attention in environmental, medical, agricultural and industrial processes. Alcohol addition plays an important role in controlling microbubble generation. The effect of n‐butanol concentration on microbubble characteristics has not been studied, thus experiments have been done to investigate the control of microbubbles in alcohol solutions.RESULTSMicrobubbles were successfully generated using a 19‐channel ceramic membrane. The bubble Sauter diameter was found to decrease with increasing n‐butanol concentration. Increasing cross flow velocity and decreasing superficial gas velocity resulted in smaller bubbles. Gas holdup and specific interfacial area was found to increase with increasing n‐butanol concentration. The volumetric mass transfer coefficient Kla was found to increase with increasing n‐butanol concentration, following the trend in specific interfacial area. Increasing cross‐flow velocity and superficial gas velocity resulted in increased Kla.CONCLUSIONSBubble characteristics in solutions with different n‐butanol concentrations are very different. Alcohol addition is an important way to generate smaller bubbles and larger gas holdup. © 2018 Society of Chemical Industry

Gas-liquid-solid volumetric mass transfer coefficient and impeller power consumptions for industrial vessel design

Waste-water treatment, fermentation, chlorination/de-chlorination and hydrogenation are processes often realized in mechanically agitated vessels. In many cases the gas-liquid mass transfer can be the limiting process in the utilization of mechanically agitated vessels. The parameter describing gas-liquid mass transfer intensity (volumetric mass transfer coefficient kLa) becomes than the key parameter. Because in fermentation processes as well as in hydrogenation ones solid particles are usually also present in gas-liquid system, we aim to study experimentally the effect of solid particles presence on kLa and power input values using reliable measuring methods. This study broadens the results on transport characteristics published in IJHMT recently (Petříček et al., 2017) [1].Measurements were conducted in a three phase multiple-impeller fermenter of i.d. 29 cm containing microparticles of the diameter 137 ± 30 μm. To cover the effect of impeller type in our results, we gradually used Rushton turbine, Pitched-blade pumping down and Techmix pumping down impellers of the diameter of 1/3 of the vessel diameter. To measure kLa using dissolved oxygen (DO) polarographic probes the Dynamic pressure method (DPM) has been chosen. We present our results in the form of dependencies of kLa on process parameters as impeller power, gas superficial velocity, impeller blade speed, etc. We used several mathematical shapes of the dependencies to find which ones will describe the kLa dependency accurately well, to be used in agitated vessels industrial design, when gas-liquid-solid system should be treated.Usually, kLa correlations are based on gassed power input and superficial gas velocity. We tested several correlation types, evaluated their empirical parameters and proposed the correlation shapes suitable for fermenter design, operating and scale-up under the conditions, where solid particles affect the interfacial mass transfer.

Experimental investigation on gas-liquid mass transfer with fast chemical reaction in microchannel

The gas-liquid two-phase flow and mass transfer with fast chemical reaction in a microchannel were investigated experimentally. Result showed that the bubble volume decreased exponentially with its movement along the channel in a quickly reactable absorbent. The volumetric mass transfer coefficient kLa increased with gas flow rate, while it was insensitive to liquid flow rate under experimental conditions, although the mass transfer coefficient kL increased with liquid flow rate. In slug-bubbly flow regime, the kL decreased when increasing gas flow rate, but inverse tendency was found for slug flow pattern. Both kL and kLa increased with the increase of absorbent concentration. A new correlation for predicting the volumetric mass transfer coefficients kLa was proposed by taking the enhancement factor E of chemical reaction into account.

Mass Transfer Study of Newtonian Fluids with Different Viscosity under Low-Frequency, High-Power Ultrasound Irradiation

In this article, the effects of liquid properties and operating conditions on gas–liquid mass transfer under ultrasound irradiation and mechanical stirring were studied and compared. Response surface methodology (RSM) was utilized for the design of experiments and evaluation of the influence of operating parameters. The maximum value of volumetric mass transfer coefficient (kLa) was found to be 0.0714 s−1 when the ultrasonic horn was located horizontally just above the gas sparger in the tank. Ultrasonic power and the position of ultrasonic horn were found to be the most significant parameters that influence kLa. Also, three empirical correlations were developed to estimate kLa considering liquid viscosity as one of the main parameters, and their estimations were compared to those estimated using existing correlations in the literature.

Volumetric Mass Transfer Coefficient in Fermenters: Scale‐up Study in Viscous Liquids

AbstractIn the design of mechanically agitated fermenters, the volumetric mass transfer coefficient kLa often becomes the key parameter. In case of viscous liquids, kLa prediction based on literature correlations suffers from a wide distribution. The aim is to provide reliable kLa correlations based on a large experimental data set obtained using the dynamic pressure method, the physical correctness of which was verified earlier. Multiple‐impeller fermenters of two scales were used. The impeller tip speed, rather than the power input, revealed to be the proper term for prediction of kLa. When the impeller power number is used, kLa values for various impeller types can be predicted by a common correlation which, based on a wide range of operational conditions, can be applied in the design.

Power consumption and mass transfer in a gas-liquid-solid stirred tank reactor with various triple-impeller combinations

Five triple-impeller combinations were used to study the effects of impeller combination on gassed power consumption and volumetric mass transfer coefficient kLa in a baffled gas-liquid-solid stirred tank reactor with air, water, and 12vol% of glass beads. The bottom impeller was chosen from two radial flow type impellers of half-elliptical-blade disk turbine (HEDT) and parabolic-blade disk turbine (PDT), and the upper two impellers were chosen from four axial flow type impellers with different blade widths and pumping modes, forming five different triple-impeller combinations: HEDT+2WHU, HEDT+2WHD, PDT+2WHD, PDT+2CBYW, and PDT+2CBYN. The experimental results show that the addition of solid particles has little effect on the relative power demand (RPD), but significant effect on kLa. kLa in a three-phase system is smaller than that in a two-phase system, and HEDT+2WHU with two up-pumping upper impellers shows the best mass transfer performance in these five triple-impeller combinations at various superficial gas velocities uG, much different from what HEDT+2WHU behaves in two-phase systems. The bottom impeller mainly influences the absolute power consumption, but the two upper impellers play a more important role on the change of RPD than the bottom impeller. The impeller combinations with a higher power number and larger projection cross-sectional area can lead to a higher kLa. The effect of operating conditions (e.g., power consumption and superficial gas velocity), the bottom impeller, the blade width and pumping mode of the two upper impellers, and solid particles were investigated and discussed in detail. To better explain the difference of mass transfer performance between impeller combinations HEDT+2WHD/U, the Eulerian-Eulerian formulation of the k-ε turbulence model with the population balance model (PBM) was used to simulate the flow field in gas-liquid systems.

Experimental and CFD–PBM approach coupled with a simplified dynamic analysis of mass transfer in phenol biodegradation in a three phase system of an aerated two-phase partitioning bioreactor for environmental applications

A three-dimensional transient modeling of a two-phase partitioning bioreactor, combining system hydrodynamics, two simultaneous mass transfer and microorganism growth is modeled using computational fluid dynamics code FLUENT 6.2. The simulation is based on standard “k–e” Reynolds-averaged Navier–Stokes model. Population balance model is implemented in order to describe gas bubble coalescence, breakage and species transport in the reaction medium and to predict oxygen volumetric mass transfer coefficient (kLa). Model results are verified against experimental data and show good agreement as 13 classes of bubble size is taking into account. Flow behavior in different operational conditions is studied. Almost at all impeller speeds and aeration intensities there were acceptable distributions of species caused by proper mixing. The magnitude of dissolved oxygen percentage in aqueous phase has a direct correlation with impeller speed and any increasing of the aeration magnitude leads to faster saturation in shorter periods of time.

Theoretical prediction of mass transfer coefficients in both gas–liquid and slurry bubble columns

The gas–liquid contact time has been defined in a new way (bubble surface-to-rate of surface formation) and the range of applicability of the penetration theory in both gas–liquid and slurry bubble columns has been examined. In both reactors, the mass transfer coefficients were predicted successfully not only in the homogeneous regime but also in the heterogeneous regime (superficial gas velocities up to 0.08ms−1).The results in the article demonstrate the importance of the geometrical characteristics (length and height) of the oblate ellipsoidal bubbles for the accurate calculation of the contact time and thus the volumetric liquid-phase mass transfer coefficient kLa. The gas–liquid interfacial area has been calculated in both reactors in the classical way, i.e. as a function of the gas holdup and inversely proportional to the Sauter-mean bubble diameter. It was found that in the gas–liquid bubble column (0.095m in ID) the modified penetration theory was applicable to tap water, 9 organic liquids (decalin, nitrobenzene, 2-propanol, 1,4-dioxane, ethanol (99%), tetralin, xylene, 1,2-dichloroethane, ethylene glycol) and two liquid mixtures (water-glycol and tetralin-ethanol). Tetralin was aerated with both nitrogen and helium, whereas xylene was aerated with hydrogen and helium. The correction factor introduced by Calderbank (1967) was found useful for improving the kLa predictions in 1,2-dichloroethane, ethanol (99%), xylene(-hydrogen) and toluene–ethanol 97.2%. In the case of a slurry bubble column, the new approach was found applicable (at low solids concentrations) to four different gas–liquid–solid systems: air–tetralin–Al2O3, air–water–Al2O3, air–water-activated carbon and air–Na2SO4–kieselguhr. It is noteworthy that in some cases (air–water-Al2O3) the new definition of the contact time was found applicable up to solids concentrations of 6.29%. In the case of a slurry bubble column, it was found that when the theoretical kLa value is multiplied by the inverse value of the correction factor the predictions improve with about 5%.Finally, in the slurry bubble column the contact time was defined on the basis of the length of the micro-eddies and the kLa values in both air–water-alumina and air–water-activated carbon systems were successfully predicted. This is also a potentially good approach.

The Influence of Optic and Polarographic Dissolved Oxygen Sensors Estimating the Volumetric Oxygen Mass Transfer Coefficient (KLa)

Aeration is usually the most energy intensive part of the wastewater treatment process. Optimizing the aeration system is essential for reducing energy costs. Field tests oriented to estimate parameters related to oxygen transfer are a common approach to compare aeration systems. The aim of this research is to assess the effect of dissolved oxygen probe lag on oxygen transfer parameter estimation. Experimental procedures regarding to process automation and control were applied to quantify dissolved oxygen probe lag. We have measured oxygen transfer in clean water, under a wide range of conditions (airflow rate, diffuser characteristics and diffuser density), with optic and polarographic sensors for dissolved oxygen measurement. The oxygen transfer was measured as per ASCE Standard procedures. Nonparametric statistical tests were used to compare the estimated volumetric mass transfer coefficient KLa with different sensors. According to the results, there is not significant influence of the probe lag (also known as time constant) or probe characteristics on the parameters used to assess oxygen transfer efficiency. This fact has great relevance in common practice of aerobic process for wastewater treatment because dissolved oxygen monitoring is used as an input for decision making related to the energy optimization in the aeration system. Findings from these tests contradict previous studies which claim that lag time in polarographic sensors for the dissolved oxygen measurement can bias estimate KLa.

Correlation for the maximum oxygen transfer capacity in shake flasks for a wide range of operating conditions and for different culture media

Characterization of shake flasks is essential to ensure a sufficient oxygen supply for aerobic microorganism. To determine the volumetric mass transfer coefficient kLa or the maximum oxygen transfer capacity OTRmax the sulfite system is commonly applied. It has been used for non-baffled shake flasks based on the assumption of a proportionality between the kLa of the sulfite system and of a biological culture. This work proves this to be valid only for shaking frequencies above 300rpm. Below the proportionality factor depends on the shaking frequency. More than 350 experiments with different concentrations of the sulfite system, 16 different media compositions and 10 different microorganisms were evaluated varying the shaking diameter (1.25–10cm), flask diameter (51–131mm), filling volume (2–160mL) and shaking frequency (100–450rpm). For the first time the properties of the culture media are coherently represented by a term based on the easily accessible osmolality. An universal consistent equation to calculate the OTRmax for non-baffled shake flasks for an exhaustive range of shaking conditions was developed and validated by experimental data. The deviations are within a remarkable narrow range of ±5mmolL−1h−1.

Investigation of extraction fraction in confined impinging jet reactors for tri-butyl-phosphate extracting butyric acid process

The extraction fraction E and overall volumetric mass transfer coefficient kLa of TBP extracting butyric acid process in confined impinging jet reactors (CIJR) with two jets were investigated. The main variables tested were the concentration of tri-butyl-phosphate (TBP) and butyric acid, the impinging velocity V, the impinging velocity ratio of two phases Vorg/Vaq, the nozzle inner diameter di and the distance L between the jet axes and the top wall of the impinging chamber. The results showed that E and kLa increase with an increase of the impinging velocity V, the concentration of TBP Corg, and the impinging velocity ratio Vorg/Vaq. However, E and kLa decrease with an increase of the inner diameter di from 1 to 2mm, the concentration of butyric acid Caq from 0.5% (v/v) to 2% (v/v). The factor L ranging from 3 to 11mm has a negligible effect on E and kLa. A correlation on these variables and kLa was proposed based on the experimental data. These results indicated good mass transfer performance of CIJR in the extraction operation.

Proton Transfer Reaction-Mass Spectrometry (PTR-MS) as a tool for the determination of mass transfer coefficients

We present an alternative technique for the measurement of mass transfer coefficients for bubble columns from the gas phase with the mass spectrometric technique of Proton Transfer Reaction-Mass Spectrometry (PTR-MS). Instead of liquid phase measurements, we apply gas phase measurements of the effluent gas phase with the PTR-mass spectrometer. The method is based on the inert gas stripping approach for the determination of Henry׳s law constant. Therein gas is bubbled through a liquid-water-compound mix, and the declining concentration of the compound in the gas phase is measured over time. For the determination of the mass transfer coefficients, the concentration over time profile is used. Experiments for determination of mass transfer coefficients were carried out in small lab scale under controlled isothermal (thermostated) conditions and with a glass frit sparger. In principle this setup could be performed offline with any detector that has a linear signal dependence over a wide concentration range. PTR-MS has the advantages of low limit of detection (ppt(v)–ppq(v)), wide linear range, and split second detection. We review the formulas for the determination of mass transfer coefficients. The relation with the equilibrium Henry׳s law constant is pointed out (extrapolation to origin considering gas holdup). We determine the overall volumetric mass transfer coefficient KLa, and moreover apply a method for the additional estimation of the liquid-side and gas-side mass transfer coefficients from KLa. Correlations of the superficial gas velocity to the gas holdup ε, the overall volumetric mass transfer coefficient KLa, the liquid side and gas phase volumetric side mass transfer coefficients kLa and kGa, as well as the ration kLa /ε are reported. The results demonstrate the suitability of PTR-MS to the determination of mass transfer coefficient for bubble columns.

Sorption of Cr(VI) by MgAl-NO3 hydrotalcite in fixed-bed column: Experiments and prediction of breakthrough curves

This study describes the sorption of Cr(VI) by MgAl-NO3 hydrotalcite in a fixed-bed column. The sorbent was prepared via coprecipitation method and characterized by XRD, FTIR, BET surface area and pHzpc. The effects of operating parameters such as bed height, flow rate and inlet concentration were investigated in continuous mode. As a result, the exhaustion time increased with the increase of bed height, decrease of flow rate and inlet concentration. A mathematical model based on the constant pattern theory and the Freundlich isotherm was applied to predict the experimental data, and to evaluate the model parameters of the fixed-bed column. The developed model describes well the breakthrough curves at various operating conditions. The calculated volumetric mass transfer coefficient KLa depends directly on these conditions. KLa increased with increasing flow rate and inlet concentration, while remained almost constant with varying bed height.

Correlation for kLa Prediction of Airlift Loop Reactors Including the Gas Phase Residence Time Effect

AbstractExperimental mass transfer data and literature data of airlift loop reactors are analyzed concerning the effect of the gas phase residence time on the volumetric mass transfer coefficient kLa. It becomes evident that a neglect of the oxygen depletion can be regarded as a diminishment of the mass transfer driving force. The latter is found to be an important cause of the mass transfer dependency on the actual apparatus height of airlift loop reactors. Therefore, a new correlation is presented that describes the volumetric mass transfer coefficients of airlift loop reactors by including the effect of gas phase transient component concentration depletion.

The effect of aeration conditions, characterized by the volumetric mass transfer coefficient KLa, on the fermentation kinetics of Bacillus thuringiensis kurstaki

The aeration is a key factor for Bacillus thuringiensis growth, sporulation and δ-endotoxins production. The objective of our work was to study the effect of aeration on the fermentation kinetics of Bacillus thuringiensis kurstaki (Btk), cultivated in a cereal milling byproduct (CMB) mono-component medium, in order to improve the δ-endotoxins productivity. Aeration conditions were systematically characterized by the volumetric mass transfer coefficient KLa. In the 6% CMB culture medium, different values of the maximal specific oxygen uptake rate were obtained at different values of KLa. For KLa of 7.2 h(-1), the growth was inhibited and the sporulation was defective. There was a linear increase of the average specific growth rate and faster sporulation and liberation of spores and δ-endotoxins crystals when KLa was increased between 13.3 h(-1) and 65.5 h(-1). Similar kinetic was observed in cultures performed at KLa equal to 65.5 h(-1) and 106.2 h(-1). The highest toxins productivity of 96.1 mg L(-1) (h)-1 was obtained in the 9% CMB culture medium for KLa of 102 h(-1). It was possible to track the evolution of the bacterial cells between vegetative growth, sporulation and liberation of mature spores by following the variation of the CO2 percent in the effluent gas.

Gas–Liquid Mass Transfer Characteristics in a Gas–Liquid–Solid Bubble Column under Elevated Pressure and Temperature

The volumetric mass transfer coefficient kLa of gases (H2, CO, CO2) and mass transfer coefficient kL on liquid paraffin side were studied using the dynamic absorption method in slurry bubble column reactors under elevated temperature and elevated pressure. Meanwhile, gas-holdup and gas–liquid interfacial area a were obtained. The effects of temperature, pressure, superficial gas velocity and solid concentration on the mass transfer coefficient were discussed. Experimental results show that the gas–liquid volumetric mass transfer coefficient kLa and interfacial area a increased with the increase of pressure, temperature, and superficial gas velocity, and decreased with the slurry concentration. The mass transfer coefficient kL increased with increasing superficial gas velocity and temperature and decreased with higher slurry concentration, while it changed slightly with pressure. According to analysis of experimental data, an empirical correlation is obtained to calculate the values of kLa for H2 (CO, CO2) in the gas–paraffin–quartz system in a bubble column under elevated temperature and elevated pressure.

The engineering sizing of the packed desorption column of hydrogen isotopes from Pb–17Li eutectic alloy. A rate based model using experimental mass transfer coefficients from a Melodie loop

The model of the desorption of hydrogen isotopes from lead lithium alloy in a packed column is derived from the first principles using the plug flow in the liquid phase either the plug flow or ideal mixing in the gas phases. Sievert's law of non-linear equilibrium is followed. The volumetric mass transfer coefficient kLa and its dependence on the liquid metal flow rate are evaluated on the basis of the Melodie loop experiments.The presented model is used for evaluation of the minimum flow rate of the purge gas for which the concentration of the isotope in the gas leaving the column is at its highest, while the driving force of the interfacial transport of the isotope is still not reduced and the tritium desorption efficiency is therefore retained. The potential effect of the axial dispersion in the gas and liquid phase is evaluated. Highlighted are the issues of the optimum packing geometric surface area, above which the efficiency starts to decrease, and of the role of the surface tension and the contact angle with regard to the wettability of the packing. On the basis of the findings related to these factors, the Mellapak 500Y and Mellapak packings with flat surfaces are recommended for the tests aiming to intensify the tritium desorption efficiency in the packed columns. The models were used for the engineering sizing of the packed columns in two breeding blanket concepts for the DEMO plant – utilizing DCLL (dual coolant lead lithium) and HCLL (helium cooled lithium lead).