Oxygen transfer to the liquid phase is perhaps the most important transport process, due to both the relatively low solubility of oxygen in water and the high demand from aerobic bioprocesses. Performing a mole balance in the liquid phase of a bioreactor yields. Its main power requirement comes from aeration, which is used to supply dissolved oxygen to the microorganisms and to maintain the solids in suspension. Determination of the volumetric oxygen transfer coefficient k l a plays an important role in the design and characterization of bioreactors. Several methods are available for determining the volumetric oxygen transfer coefficient in bioreactors, though their application in industrial bioprocess has been limited.
Membrane bioreactor mbr is a promising alternative to conventional wastewater treatment methods. Read this article to learn about volumetric oxygen transfer coefficient kla. To be practically useful, mass transfer measurements made in nonfermenting systems must be consistent with observed microbial respiration rates. The latter is an important factor for aerobic cultures. The effect of surfactants on oxygen transfer is also studied and a method to determine the floc volume of activated sludge is developed. Cell culture scaleup in stirredtank singleuse bioreactors. Mar 25, 2009 the mass transfer coefficient k l a determines the magnitude of the otr. The aim of these experiments is to study the oxygen mass transfer rate through the mass transfer coefficient, for a stirred bioreactor and different fermentation broths, using a large domain of. A polarographic dissolved oxygen electrode is used. Here i provide information for those who are unfamiliar with the measurement method andor issues that must be considered when making these measurements. Gasliquid mass transfer in bioreactors is characterized in terms of the overall volumetric oxygen transfer coefficient kla and the oxygen uptake rate our.
Pdf development of a model to determine mass transfer. Simultaneous determination of oxygen consumption rate. Applicability of sterilizable oxygen electrode response. Aeration step method for kla measurement under growth. The concentration of oxygen at the surface of air bubbles is high compared with that in the bulk of the liquid. Pdf variables affecting the oxygen mass transfer in bioreactors. Bioprocess development upstream and downstream technologies.
Pdf control of dissolved oxygen in stirred bioreactors. Oxygen mass transfer studies on batch cultivation of p. In addition, in submerged mbrs, aeration is used for membrane. Pdf a twocompartment model is presented to calculate the oxygen. Cells obtain their oxygen in free and noncompound forms, called dissolved oxygen do.
For example, singh studied oxygen transfer in a 20l bag at 50% fill on a system with a rocking capacity of 540 rpm and 510, and the maximum k l a observed was 4 h 1 2. The correct measurement andor prediction of the volumetric mass transfer coefficient, kla, is a crucial step in the design, operation and scaleup of bioreactors. Development of a model to determine mass transfer coefficient. Scalability in laboratory bioreactors based on constant. The volumetric mass transfer coefficient k l a describes the efficiency with which oxygen can be delivered to a bioreactor culture for a given set of parameter conditions. Jan 07, 20 in such cases, the volumetric oxygen transfer coefficient, k l a, must be known in order to carry out the design and scale up of bioreactors. Oxygen mass transfer in bioreactors involves many masstransfer resistances.
Using experimental data created by hunter and vogelaar, the formula precisely reproduces experimental results for the standardized kla at 20 c, comparatively better than the current model used by asce. Oxygen transfer, mixing time and gas hold up characterization in a hybrid bioreactor 5 d d l h h. Sparger and surface gas transfer for cell culture bioreactors. For larger bioreactors, the surface oxygen transfer is much smaller than the sparger oxygen transfer, and can be neglected during sparging. Index i refers to values at the gasliquid interface because interfacial concentrations are not directly measureable, it is. Effects of oxygen transfer coefficient on dihydroxyacetone. This property plays an essential role in the oxygen transfer rate in sparged bioreactors due to its effect on the gasliquid mass transfer coefficients and, as a consequence, the yields and. There are many techniques for measuring oxygen concentration and otr in bioreactors. This research closely examined the airtoliquid oxygen mass transfer coefficient.
Bioreactor scaleup and oxygen transfer rate in microbial. Enhancement of oxygen mass transfer and gas holdup using. Biomass effects on oxygen transfer in membrane bioreactors. In batch and fedbatch cultivations the operating conditions change significantly which may cause tuning problems. Providing sufficient oxygen and removing carbon dioxide are important in the design and operation of aerobic bioreactors. Oxygen mass transfer coefficient gasliquid contact is a matter of decisive importance for describing systems involving biological processes. Understanding the impact of aeration and thus the dissolution of oxygen into the bioreactor growth media for uptake by the production cell line is. Nowadays, bubble columns are studied as an efficient photobioreactor for production of microalgae 57. Simultaneous determination of oxygen consumption rate and. Nov 12, 2010 several methods are available for determining the volumetric oxygen transfer coefficient in bioreactors, though their application in industrial bioprocess has been limited. The volumetric mass transfer coefficient k l a is often used in order to compare the efficiency of bioreactors and as an important scaleup factor.
The objective of this paper is to present an experimentally validated mechanistic model to predict the oxygen transfer rate coefficient kla in aeration tanks for different water temperatures. Pdf variables affecting the oxygen mass transfer in. Novel and new concept to increase oxygen transfer in bioreactors. Oxygen transfer and fragmentation of aspergillus niger. The studies on the oxygen mass transfer coefficient in a. Also, a simple modified sulfite method for volumetric oxygen transfer coefficient k l a determination was developed and the experimental data were correlated with the gassed power p g by using wellknown correlations presented in the literature. In the first region, below 300 rpm, the slope is much lower. Applications of gasliquid transport with reaction gasliquid mass transfer in bioreactors microbial cells often grown aerobically in stirred tank reactors oxygen supply is often limiting x d. However this process is still underused due to its high running costs. The oxygen transfer in bioreactors with slurries having a yield stress was investigated. Zirconia, electrochemical, infrared, ultrasonic and laser cells are used to measure oxygen concentration in the liquid medium.
This report discusses control of dissolved oxygen in a bioreactor where the oxygen supply is manipulated using the stirrer speed. Published literatures showed that adding an organic phase such as hydrocarbons or vegetable oil could increase the k l a. Oxygen mass transfer into an aqueous liquid phase is enhanced in the presence of nanoparticles, as shown in figure 1. If oxygen is limited, cell growth and product formation can be affected. Assessment of kla oxygen transfer coefficient 6 methods. The methodology is based on modifications of the classical dynamic gassingin method and the steadystate mass balance method for obtaining the values k l a and our, respectively. Experimental data shown in figure 4 were fitte d to a correlation of the type of equation 1 and.
Since it is extremely difficult, if not impossible, to measure k l and the amount of bubble transfer area in a bioreactor or fermenter, an engineering parameter known as volumetric oxygen transfer coefficient, expressed by k l a, has been used to represent volumetric oxygen transfer coefficient as. The present work proposes a new aeration step method for k l a evaluation in pneumatic. Measurement of the oxygen transfer coefficient k l a. The mass balance for the dissolved oxygen in the wellmixed liquid phase, in the absence of biomass or with nonrespiring cells when biochemical reactions do not take place, can be established as follows.
Among all methods available, few techniques are suitable for the determination of k l a in pneumatic bioreactors during the course of cultivations. Aspergillus niger, biobased products, bioreactors, cell structures, energy use and consumption, hydrodynamics, mass transfer, metabolites, microorganisms, models, oxygen, pellets. Oxygen mass transfer rate in a pressurized labscale stirred bioreactor oxygen mass transfer from air to the liquid phase in bioreactors with aerobic cultureshaslongbeena serious impairmentto theproductivityofvarious bioprocesses. Oxygen transfer is a major factor influencing the efficient and economic operation of all aerobic bioprocesses, including mbrs. Volumetric mass transfer coefficient k l a is an important parameter in bioreactors handling viscous fermentations such as xanthan gum production, as it affects the reactor performance and productivity. As a result, such bioreactors might be both poorly mixed and also unable to provide the higher oxygen uptake rates demanded by more intensive. A torque meter has been developed for determining the power consumption in a bench stirred tank. Determination of power consumption and volumetric oxygen. With an increasing organic fraction, the mass transfer coefficient decreases, whereas. Techniques for oxygen transfer measurement in bioreactors. Oxygen transfer coefficient n kinematic viscosity k l a specific oxygen mass transfer coefficient z random number l e kolmogorov length scale r l density of liquid phase m torque t nn, t nt stress tensor, nn normal stress, nt shear stress m g molar mass of gas phase x reynolds stress tensor n molar flux mathematic symbols and indices. They can be conveniently classified into three major types based on the presence or absence of oxygen and requirement of stirring. Influence of volumetric oxygen transfer coefficient kla on.
In bioreactors, a number of methods are available for estimation the overall volumetric oxygen mass transfer coefficient. The oxygen transfer rate otr is influenced by the physical properties of the gas and liquid, operational conditions, geometric parameters, and the consumption rate by the cells. Knowledge of kla the volumetric mass transfer coefficient that describes the efficiency with which oxygen can be delivered to a bioreactor for a given set of operating conditions is not new. Gasliquid mass transfer coefficients in reactors depend largely on gas flow rate bubble diameter gas holdup bubble columns contd accurate estimation of the masstransfer coefficient is difficult exact bubble sizes and liquid circulation patterns are impossible to predict.
Pdf oxygen transfer in production scale bioreactor researchgate. The microbial growth in a bioreactor depends upon the oxygen transfer rate otr. Prediction of gasliquid mass transfer coefficient in. Oxygen mass transfer correlation for a rockingmotion. Development of a model to determine mass transfer coefficient and oxygen solubility in bioreactors article pdf available in heliyon 32. A new approach is proposed for the simultaneous determination of the volumetric oxygen transfer coefficient k l a and the oxygen uptake rate our in bioreactors. The oxygen mass transfer rate in a bioreactor depends on.
The oxygen volumetric mass transfer coefficient k l a was described by a function of the air pressure in a stirred lab. Oxygen transfer is often the ratelimiting step in the aerobic bioprocess due to the low solubility of oxygen in the medium. The concentration of dissolved oxygen in fermentation broth is affected by the oxygen transfer rate otr which relates to agitation speed and aeration rate and the oxygen uptake rate our from the microorganisms. Oxygen transfer, mixing time and gas hold up characterization in a hybrid bioreactor 3 was 0. Among these, resistance of the gas liquid interfacial area a and liquid film resistance kl are usually the ratelimiting steps for transfer of oxygen to or from the bulk of the liquid phase. A similar equation can be written for oxygen surface transfer, using the oxygen mass transfer coefficient for the surface k l,oxa s and the driving force from the headspace gas o 2o 2 s. Equation 1 can be though of as providing a definition for the mass transfer coefficient. Classification of bioreactors there are numerous types of bioreactors batch, sequence, continuously stirred tanks, anaerobic contact processes, anaerobic filters, etc. Subsurface aeration systems, which release bubbles below the surface, always have higher saturation concentrations than the text book values of do. Power consumption measurements in ungassed and gassed systems were obtained at different agitation and aeration conditions, for newtonian and non. In this study, batch fermentations in stirred tank bioreactor stb and airlift.
The oxygen transfer coefficient, kla, increased from 0. One of the most important functions of bioreactors is providing dissolved oxygen to cells continuously through a process called aeration. Analysis using a linearized process model shows that the process dynamics is mainly affected by changes in the volumetric oxygen transfer coefficient. Generally, the major responsibilities of a bioreactor are to provide a biomechanical and a biochemical environment that controls nutrient and oxygen transfer to the cells and metabolic products from the cells 11. Oxygen is the most essential requirement for aerobic bioprocesses.
Lka is a gas transfer coefficient,a measurement of the capacity of the bioreactor to transfer oxygen into the cultures. In cell culture, oxygen is a key substrate for growth, production, and maintenance activities. A polarographic dissolved oxygen electrode is used to. Among these, resistance of the gasliquid interfacial area a and liquid film resistance kl are usually the ratelimiting steps for transfer of oxygen to or from the bulk of the liquid phase. An important example of mass transfer in bioprocessing is the supply of oxygen in fermenters for aerobic culture. In view of mass transfer dynamic measurements in bioreactors, the transient response of two steam sterilizable oxygen electrodes a polarographic electrode with a double membrane and a galvanic conventional one has been studied in the gas phase as well as in the liquid phase. In such cases, the volumetric oxygen transfer coefficient, k l a, must be known in order to carry out the design and scale up of bioreactors. Oxygen transfer, mixing time and gas holdup characterization. Measurement of volumetric mass transfer coefficient in. The methodology is based on modifications of the classical dynamic gassing in method and the steadystate mass balance method for obtaining the values kla and our, respectively. Novel and new concept to increase oxygen transfer in.
Oxygen transfer rate an overview sciencedirect topics. The mass transfer of oxygen transfer is often a limiting factor in bioreactors. To be practically useful, mass transfer measurements made in nonfermenting systems must be consistent with. Oxygen plays an important role in aerobic bioprocesses and it is often the limiting factor of the bioreactor. Chisti department of chemical engineering, university of almer.
Biomass characteristics, aeration and oxygen transfer in. Oxygen mass transfer rate in a pressurized labscale stirred. In such cases, the volumetric oxygen transfer coefficient. Jun 23, 2018 furthermore, the different bioreactor system designs studied may explain the oxygen mass transfer coefficient k l a results that cannot be compared adequately. In this work, a critical distinction is made between the oxygen mass transfer coefficient, k l a, and the oxygen mass transfer rate. Among the fermentation processes, there are main factors to optimize and control to obtain the best yield and productivity such as ph, temperature and dissolved oxygen concentration. Homogenisation and oxygen transfer rates in large agitated. The impact of aeration on cell culture in bioreactors. L bubble column with simulated fermentation broths, the theological properties of which were represented by the casson model, were measured. A novel method of simulating oxygen mass transfer in two. Therefore oxygen is an important requirement in aerobic processes like.
Due to the fact that oxygen has a very low solubility in an. The methodology is based on modifications of the classical dynamic gassing in method and the steadystate mass balance method for obtaining the values k l a and our, respectively. The majority of fermentation processes are aerobic. Oxygen transfer and fragmentation of aspergillus niger pellets in stirred tank and concentricduct airlift bioreactors author. Because of concern for cell damage, very low agitation energy inputs have been used in industrial animal cell bioreactors, typical values being two orders of magnitude less than those found in bacterial fermentations. The rate of oxygen transfer from air bubble to the liquid phase may be described by the equation. In biotechnology, oxygen mass transfer is a key parameter involved in the design and operation of bioreactors and it can be analyzed by means of the oxygen mass transfer coefficient k l a. The present study opted for palm oil as the organic phase as it is.
An increase of the oxygen mass transfer rate otr can be the key to overcome oxygen limitation. Mass transfer between phases may often become the limiting step of the overall process rate. A new approach is proposed for the simultaneous determination of the volumetric oxygen transfer coefficient kla and the oxygen uptake rate our in bioreactors. The second term describes the oxygen consumption due to the biological activity. In that equation, j 0 is the molar flux of oxygen molm 2 s through the gasliquid interface, k g and k l are the local mass transfer coefficients, p g is the oxygen partial pressure in the gas phase, and c l is the dissolved oxygen concentration in the liquid. Simultaneous determination of oxygen consumption rate and volumetric oxygen transfer coefficient in pneumatically agitated bioreactors j. Therefore, 192 grams of oxygen are required for the complete oxidation of 180 grams of glucose. Suresh and others published variables affecting the oxygen mass transfer in bioreactors find, read and cite all the research you need on researchgate. The device has been bonded in the stirrer shaft inside a commercial bench fermentor, in order to avoid frictional losses in the mechanical seal. The mass transfer coefficient k l a determines the magnitude of the otr. The time required to reach saturation is reduced by approximately 25% in the presence of a nanoparticle mass fraction of. The changes of the volumetric oxygen transfer coefficient, the oxygen uptake rate and the specific oxygen consumption rate for suspension cultures of taxus media cells in a 10 l bioreactor were. The residence time of the gas in dispersion tr, and average bubble rising velocity ub in the riser,were calculated using eqs.
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