Estimation of oxygen transfer in soil slurry bioreactor

The apparent volumetric O transfer coefficient in a soil slurry bioreactor was significantly affected by the particle size of the soil and its clay content but less affected by the concentration of organic matter. The k L a values in the slurry of 40% (w/v) soil content ranged from 60% to 80% of that in water. O requirement was estimated for a bio-remediation: O was limiting in heavily contaminated soil and in soil with high clay content.     

Hydrodynamics, mass transfer and rheological studies of gibberellic acid production in an airlift bioreactor

Although a lot of research has been done into modelling microbial processes, the applicability of these concepts to problems specific for bioreactor design and optimization of process conditions is limited. This is partly due to the tendency to separate the two essential factors of bioreactor modelling, i.e. physical transport processes and microbial kinetics. The deficiencies of these models become especially evident in industrial production processes where O₂ supply is likely to become the limiting factor, e.g. production of gibberellic acid and other organic acids. Hydrodynamics, mass transfer and rheology of gibberellic acid production by Gibberella fujikuroi in an airlift bioreactor is presented in this work. Important hydrodynamic parameters such as gas holdup, liquid velocity in the riser and in the downcomer, and mixing time were determined and correlated with superficial gas velocity in the riser. Mass transfer was studied evaluating the volumetric mass transfer coefficient, which was determined as a function of superficial gas velocity in the riser and as a function of fermentation time. Culture medium rheology was studied through fermentation time and allowed to explain the volumetric mass transfer coefficient behaviour. Rheological behaviour was explained in terms of changes in the morphology of the fungus. Finally, rheological studies let us obtain correlations for gas holdup and volumetric mass transfer coefficient estimation using the superficial gas velocity in the riser and the culture medium apparent viscosity.     

Hydrodynamics, mass transfer, and yeast culture performance of a column bioreactor with ejector

A bubble column fitted with an ejector has been tested for its physical and biological performance. The axial diffusion coefficient of the liquid phase in the presence of electrolytes and ethanol was measured by a stimulus-response technique with subsequent evaluation by means of a diffusion model. In contrast to ordinary bubble columns, the coefficient of axial mixing is inversely dependent on the superficial air velocity. The liquid velocity acts in an opposite direction to the backmixing flow in the column. The measurement of volumetric oxygen transfer coefficient in the presence of electrolytes and ethanol was performed using a dynamic gassing-in method adapted for a column. The data were correlated with the superficial air and liquid velocities, total power input, and power for aeration and mixing; the economy coefficient of oxygen transfer was used for finding an optimum ratio of power for aeration and pumping. Growth experiments with Candida utilis on ethanol confirmed some of the above results. Biomass productivity of 2.5 g L(-1) h(-1) testifies about a good transfer capability of the column. Columns fitted with pneumatic and/or hydraulic energy input may be promising for aerobic fermentations considering their mass transfer and mixing characteristics.     

Mixing and oxygen transfer characteristics of a microplate bioreactor with surface-attached microposts

Bioprocess optimization for cell-based therapies is a resource heavy activity. To reduce the associated cost and time, process development may be carried out in small volume systems, with the caveat that such systems be predictive for process scale-up. The transport of oxygen from the gas phase into the culture medium, characterized using the volumetric mass transfer coefficient, k_La, has been identified as a critical parameter for predictive process scale-up. Here, we describe the development of a 96-well microplate with integrated Redbud Posts to provide mixing and enhanced k_La. Mixing in the microplate is characterized by observation of dyes and analyzed using the relative mixing index (RMI). The k_La is measured via dynamic gassing out method. Actuating Redbud Posts are shown to increase rate of planar homogeneity (2 min) verse diffusion alone (120 min) and increase oxygenation, with increasing stirrer speed (3500-9000 rpm) and decreasing fill volume (150-350 μL) leading to an increase in k_La (4-88 h⁻¹). Significant increase in Chinese Hamster Ovary growth in Redbud Labs vessel (580,000 cells mL^-1) versus the control (420,000 cells mL^-1); t(12.814) = 8.3678, p ≤ .001), and CD4⁺ Naïve cell growth in the microbioreactor indicates the potential for this technology in early stage bioprocess development and optimization.     

Hydrodynamic characteristics and overall volumetric oxygen transfer coefficient of a new multi-environment bioreactor

The hydrodynamic characteristics and the overall volumetric oxygen transfer coefficient of a new multi-environment bioreactor which is an integrated part of a wastewater treatment system, called BioCAST, were studied. This bioreactor contains several zones with different environmental conditions including aerobic, microaerophilic and anoxic, designed to increase the contaminant removal capacity of the treatment system. The multi-environment bioreactor is designed based on the concept of airlift reactors where liquid is circulated through the zones with different environmental conditions. The presence of openings between the aerobic zone and the adjacent oxygen-depleted microaerophilic zone changes the hydrodynamic properties of this bioreactor compared to the conventional airlift designs. The impact of operating and process parameters, notably the hydraulic retention time (HRT) and superficial gas velocity (U _G), on the hydrodynamics and mass transfer characteristics of the system was examined. The results showed that liquid circulation velocity (V _L), gas holdup (ε) and overall volumetric oxygen transfer coefficient ( $ k_{\text{L}} a_{\text{L}} $ ) increase with the increase of superficial gas velocity (U _G), while the mean circulation time (t _c) decreases with the increase of superficial gas velocity. The mean circulation time between the aerobic zone (riser) and microaerophilic zone (downcomer) is a stronger function of the superficial gas velocity for the smaller openings (1/2 in.) between the two zones, while for the larger opening (1 in.) the mean circulation time is almost independent of U _G for U _G ≥ 0.023 m/s. The smaller openings between the two zones provide higher mass transfer coefficient and better zone generation which will contribute to improved performance of the system during treatment operations.     

Fluid mixing and oxygen transfer in cell suspensions ofTaxus chinensis in a novel stirred bioreactor

In high-density plant cell cultures, mixing and mass transfer are two key issues, which should be emphasized for process optimization. In this work, both mixing and oxygen transfer characteristics of cell suspensions ofTaxus chinensis were studied in a new centrifugal impeller bioreactor with a working volume of 1.2 L. The mixing time (t _M) and the volumetric oxygen transfer coefficient (K _L a) under different operational conditions were determined in both tap water and cell suspensions of 100–400 g fresh weight/L (i.e., 5.65–23.1 g DW/L). At an aeration rate of 0.1 L/min,t _M decreased from 10.6s at 30 rpm to 2.89 s at 200 rpm under 100 g FW/L, and from 9.63 s (120 rpm) to 4.05 s (300 rpm) under 400 g FW/L. Compared with the effect of agitation, aeration was less significant to the suspension mixing. At a relatively high agitation speed (e.g., 200 rpm),t _M remained almost the same even though aeration rate was changed from 0.1 to 0.4 L/min. Thet _M value increased slowly from 3.98 to 5.26 s at 120 rpm when the cell density was raised from 100 to 250 g FW/L. A rapid increase of botht _M and the suspension viscosity was observed at a cell density above 300 g FW/L. As expected, theK _L a value increased with an increase of aeration rate and agitation speed, but decreased with an increase of cell density. The quantitative data obtained here are useful to investigate the effect of mixing stress on the cell physiology and metabolism ofTaxus chinensis in the bioreactor. This paper is dedicated by JJZ to his colleague Prof. Jun-Tang Yu on the occasion of his 70 birthday.     

Gas hold-up and oxygen mass transfer in three pneumatic bioreactors operating with sugarcane bagasse suspensions

Sugarcane bagasse is a low-cost and abundant by-product generated by the bioethanol industry, and is a potential substrate for cellulolytic enzyme production. The aim of this work was to evaluate the effects of air flow rate (Q _AIR), solids loading (%_S), sugarcane bagasse type, and particle size on the gas hold-up (ε _G) and volumetric oxygen transfer coefficient (k _L a) in three different pneumatic bioreactors, using response surface methodology. Concentric tube airlift (CTA), split-cylinder airlift (SCA), and bubble column (BC) bioreactor types were tested. Q _AIR and  %_S affected oxygen mass transfer positively and negatively, respectively, while sugarcane bagasse type and particle size (within the range studied) did not influence k _L a. Using large particles of untreated sugarcane bagasse, the loop-type bioreactors (CTA and SCA) exhibited higher mass transfer, compared to the BC reactor. At higher  %_S, SCA presented a higher k _L a value (0.0448 s^?1) than CTA, and the best operational conditions in terms of oxygen mass transfer were achieved for  %_S < 10.0 g L^?1 and Q _AIR > 27.0 L min^?1. These results demonstrated that pneumatic bioreactors can provide elevated oxygen transfer in the presence of vegetal biomass, making them an excellent option for use in three-phase systems for cellulolytic enzyme production by filamentous fungi.     

Kinetics of biodegradation of p-xylene and naphthalene and oxygen transfer in a novel airlift immobilized bioreactor

The scope of this study included the biodegradation performance and the rate of oxygen transfer in a pilot-scale immobilized soil bioreactor system (ISBR) of 10-L working volume. The ISBR was inoculated with an acclimatized population of contaminant degrading microorganisms. Immobilization of microorganisms on a non-woven polyester textile developed the active biofilm, thereby obtaining biodegradation rates of 81 mg/L x h and 40 mg/L x h for p-xylene and naphthalene, respectively. Monod kinetic model was found to be suitable to correlate the experimental data obtained during the course of batch and continuous operations. Oxygen uptake and transfer rates were determined during the batch biodegradation process. The dynamic gassing-out method was used to determine the oxygen uptake rate (OUR) and volumetric oxygen mass transfer, K(L) a. The maximum volumetric OUR of 255 mg O(2)/L x h occurred approximately at 720-722 h after inoculation, when the dry weight of biomass concentration was 0.67 g/L.     

Performance of bench-scale membrane bioreactor under real work conditions using pure oxygen: viscosity and oxygen transfer analysis

Pure oxygen to supply the aerobic condition was used in the performance of a bench-scale submerged membrane bioreactor (MBR). The pilot plant was located in the wastewater treatment plant of the city of Granada (Spain) and the experimental work was divided into two stages (Unsteady state and steady state conditions). Operation parameters (MLSS, MLVSS and dissolved oxygen concentration) and physical characteristics (temperature, conductivity, pH, COD and BOD₅) were daily monitored. The results showed the capacity of the MBR systems to remove organic material under a hydraulic retention time of 18.46 h and sludge retention time of 18.6 days. Therefore, Viscosity of the sludge and αkLa-factor of the aeration, were determinate in the steady stage condition to understand the behavior of the system when pure oxygen has been used to supply the aerobic conditions of the MBR system showed an alpha-factor of 0.238 when the viscosity of the system was 4.04 Cp.     

Characterization of oxygen transfer in a membrane-aerated hollow-fibre bioreactor using modified microcoaxial needle electrodes

In this work the volumetric O₂ transfer coefficient (OTC) through a membrane of a miniaturized hollow-fibre bioreactor was measured by the use of modified O₂ microaxial needle electrodes. Before measurment, available electrodes were modified by inserting and gluering them in thin galss capillaries to avoid damage. No differences in the behaviour of the electrodes occurred in comparison to the non-modified electrodes. These modified electrodes allowed O₂ partial pressure measurement in the 0.8-mm-high extracapillary space (ECS) of the bioreactor with high sensitivity and reliability. O₂ measurements were carried out the two ports of the ECS at different insertion depths. The results of the measurements showed a homogenous O₂ supply during variation of the radial co-coordinate of the electrode. In addition to these results, an increase in the local supply in the direction of medium flow was observed . The calculated mean OTC (47–63 h^–1) gave extremely improved O₂ transfer due to membrane aeration compared to conventional hallow-fibre systems and other bioreactors used in animal-cell culture technology. The improved OTC and the small ECS volume (4.3 ml) makes this culture system suitable for the cultivation of primary cells with tissue-like densities.     

Characterization and improvement of oxygen transfer in pilot plant external air-lift bioreactor for mycelial biomass production

The oxygen transfer dynamics in a pilot plant external air-lift bioreactor (EALB) during the cultivation of mycelial biomass were characterized with respect to hydrodynamic parameters of gas holdup (), oxygen transfer coefficient (K_La) and superficial gas velocity (U _g), and dissolved oxygen (DO). An increased flow rate of air supply was required to meet the increased oxygen demand with mycelial biomass growth. Consequently, an increase in air flow rate led to an increase in , K_La and the DO level. The enhancement of oxygen transfer rate in the cultivated broth system, however, was limited with highly increased viscosity of the mycelial broth. An increase in air flow rate from 1.25 to 2.00 v/v/m resulted in a low increment of oxygen transfer. The newly designed pilot plant EALB with two air spargers significantly improved processing reliability, aeration rate and K_La. The pilot plant EALB process, operated under a top pressure from 0 to 1.0 bars, also demonstrated a significant improvement of oxygenation efficiency by more than 20% in DO and K_La. The performance of the two sparger EALB process under top pressure demonstrated an efficient and economical aerobic system with fast mycelial growth and high biomass productivity in mycelial biomass production and wastewater treatment.     

Polysaccharide concentration and molecular weight effects on the oxygen mass transfer in a reciprocating plate bioreactor

In most polysaccharide fermentations, the nature of the fermentation broth changes drastically with time and, as a result, the overall oxygen mass transfer coefficient (K(L)a) can vary by orders of magnitude. To obtain a better understanding of this phenomenon, an experimental program was devised to study the respective influence of molecular weight and concentration of dextran solutions on K(L)a. Experiments were conducted in a reciprocating plate bioreactor. This bioreactor uses a stack of perforated plates that is reciprocated axially in the column and it is therefore well suited for mixing viscous liquid broths and providing uniform overall mass transfer coefficients. The variation of K(L)a with the power input per unit volume and the superficial gas velocity were obtained for three ranges of molecular weights and five concentrations of dextran. In every medium, two regimes of operation were observed as a function of the power input per unit volume: a first regime, at low power inputs per unit volume where K(L)a remains constant until a threshold of power input is attained; and a second regime, which is characterized by a steep increase of K(L)a as a function of the power input per unit volume. The presence of dissolved biological macromolecules, not only because of their effect on the rheology of the medium but also because their effect on the gas-liquid interface, has a significant impact on K(L)a. It was found that, generally, small concentrations of polysaccharide favor oxygen mass transfer despite the increase in medium viscosity. However, the respective influence of polysaccharide concentration and molecular weight was different for the two regimes of operation. (c) 1996 John Wiley & Sons, Inc.     

Comparative analysis of oxygen transfer rate distribution in stirred bioreactor for simulated and real fermentation broths

Study of the distribution of the oxygen mass transfer coefficient, k _l a, for a stirred bioreactor and simulated (pseudoplastic solutions of carboxymethylcellulose sodium salt) bacterial (P. shermanii), yeast (S. cerevisiae), and fungal (P. chrysogenum free mycelia) broths indicated significant variation of transfer rate with bioreactor height. The magnitude of the influence of the considered factors differed from one region to another. As a consequence of cell adsorption to bubble surface, the results indicated the impossibility of achieving a uniform oxygen transfer rate throughout the whole bulk of the microbial broth, even when respecting the conditions for uniform mixing. Owing to the different affinity of biomass for bubble surface, the positive influence of power input on k _l a is more important for fungal broths, while increasing aeration is favorable only for simulated, bacterial and yeast broths. The influence of the considered factors on k _l a were included in mathematical correlations established based on experimental data. For all considered positions, the proposed equations for real broths have the general expression k_l a = aC_X^b ( \fracP_a V )^g v_S^d , k_{\rm l} a = \alpha C_{\rm X}^{\beta } \left( {{\frac{{P_{\rm a} }}{V}}} \right)^{\gamma } v_{\rm S}^{\delta } , exhibiting good agreement with experimental results (with maximum deviations of ±10.7% for simulated broths, ±8.4% for P. shermanii, ±9.3% for S. cerevisiae, and ±6.6% for P. chrysogenum).     

Hydrodynamics and mixing in down flow jet loop bioreactor with a non-Newtonian fluid

Gas holdup and liquid circulation time were measured in a down flow jet loop bioreactor with a non-Newtonian fluid. It was observed that the circulation time decreases with increase in nozzle diameter, draft tube to column diameter ratio and shear thinning of the media. The gas holdup increases with increase in gas and liquid velocities. The optimum draft tube to column diameter ratio was found to be 0.438. Correlations for gas holdup and circulation time involving operational and geometrical variables were presented.     

Study of the oxygen transfer in a disposable flexible bioreactor with surface aeration in vibrated medium

The oxygen mass transfer is a critical design parameter for most bioreactors. It can be described and analyzed by means of the volumetric mass transfer coefficient K _L a. This coefficient is affected by many factors such as geometrical and operational characteristics of the vessels, type, media composition, rheology and microorganism’s morphology and concentration. In this study, we aim to develop and characterize a new culture system based on the surface aeration of a flexible, single-used bioreactor fixed on a vibrating table. In this context, the K _L a was evaluated using a large domain of operating variables such as vibration frequency of the table, overpressure inside the pouch and viscosity of the liquid. A novel method for K _L a determination based on the equilibrium state between oxygen uptake rate and oxygen transfer rate of the system at given conditions was also developed using resting cells of baker’s fresh yeast with a measured oxygen uptake rate of 21 mg g⁻¹ h⁻¹ (at 30°C). The effect of the vibration frequency on the oxygen transfer performance was studied for frequencies ranging from 15 to 30 Hz, and a maximal K _L a of 80 h⁻¹ was recorded at 30 Hz. A rheological study of the medium added with carboxymethylcellulose at different concentrations and the effect of the liquid viscosity on K _L a were determined. Finally, the mixing time of the system was also measured using the pH method.     

Trickle-bed root culture bioreactor design and scale-up: growth, fluid-dynamics, and oxygen mass transfer

Trickle-bed root culture reactors are shown to achieve tissue concentrations as high as 36 g DW/L (752 g FW/L) at a scale of 14 L. Root growth rate in a 1.6-L reactor configuration with improved operational conditions is shown to be indistinguishable from the laboratory-scale benchmark, the shaker flask (mu=0.33 day(-1)). These results demonstrate that trickle-bed reactor systems can sustain tissue concentrations, growth rates and volumetric biomass productivities substantially higher than other reported bioreactor configurations. Mass transfer and fluid dynamics are characterized in trickle-bed root reactors to identify appropriate operating conditions and scale-up criteria. Root tissue respiration goes through a minimum with increasing liquid flow, which is qualitatively consistent with traditional trickle-bed performance. However, liquid hold-up is much higher than traditional trickle-beds and alternative correlations based on liquid hold-up per unit tissue mass are required to account for large changes in biomass volume fraction. Bioreactor characterization is sufficient to carry out preliminary design calculations that indicate scale-up feasibility to at least 10,000 liters.     

Oxygen transfer in a pulse bioreactor

Oxygen transfer in a novel pulse bioreactor has been evaluated. The agitator consists of a series of alternately fixed and movable parallel plates mounted so that the movable plates vibrate at 30 Hz causing a pulsating fluid motion. Pure oxygen, at pressures up to 5 atm, diffuses through silicone rubber tubing that also vibrates at 30 or 60 Hz. The main feature of this bioreactor is high oxygen transfer with low shear to prevent damage to fragile animal cell membranes. We estimate that sufficient oxygen can be supplied to support over 10(8) cells/mL of human diploid foreskin cells growing on microcarriers. (c) 1993 John Wiley & Sons, Inc.     

Hydrodynamics and mass transfer in an airlift loop fermentor

Summary The hydrodynamics and mass transfer behaviour of an airlift fermentor with an external loop (height 10m) has been investigated by measuring gas and liquid velocities, gas hold-up, liquid mixing and oxygen transfer coefficients. Liquid phase properties, i.e., ionic strength, viscosity and surface tension have been varied by altering the fermentation media. Results are compared with those from bubble column experiments performed in the same unit. It is shown, that more uniform two-phase flow in the airlift leads to advantages in scale-up and operation.Nomenclature a Specific interfacial area per volume of dispersion (m²/m³) - c Local concentration of tracer (kmol/m³) - c Concentration of tracer at infinite time (kmol/m³) - C_L Concentration of oxygen in the liquid bulk (kmol/m³) - C_L ^* Concentration of oxygen in the interface (kmol/m³) - D_ax Axial dispersion coefficient (cm²/s) - I Ionic strength (kmol/m³) - i Inhomogeneity [defined in Eq. (2)] - Rate of oxygen transfer (kmol/s) - t_c Circulation time (s) - t_M Mixing time (s) - V_R Volume of gas-liquid dispersion (m³) - V_SG Superficial gas velocity in up-flow column (m/s) Greek letter symbols _L Oxygen transfer coefficient (m/s) - Dynamic viscosity (m Pa s) - Surface tension (m N/m) Presented at the First European Congress on Biotechnology, Interlaken, September 25–29, 1978     

Hydrodynamics and mass transfer in miniaturized bubble column bioreactors

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

     

Hydrodynamics and mass transfer in a tubular airlift photobioreactor

In photobioreactors, which are usually operated under light limitation,sufficient dissolved inorganic carbon must be provided to avoid carbonlimitation. Efficient mass transfer of CO₂ into the culture mediumisdesirable since undissolved CO₂ is lost by outgassing. Mass transferof O₂ out of the system is also an important consideration, due tothe need to remove photosynthetically-derived O₂ before it reachesinhibitory concentrations. Hydrodynamics (mixing characteristics) are afunctionof reactor geometry and operating conditions (e.g. gas and liquid flow rates),and are a principal determinant of the light regime experienced by the culture.This in turn affects photosynthetic efficiency, productivity, and cellcomposition. This paper describes the mass transfer and hydrodynamics within anear-horizontal tubular photobioreactor. The volume, shape and velocity ofbubbles, gas hold-up, liquid velocity, slip velocity, axial dispersion,Reynoldsnumber, mixing time, and mass transfer coefficients were determined intapwater,seawater, and algal culture medium. Gas hold-up values resembled those ofvertical bubble columns, and the hydraulic regime could be characterized asplug-flow with medium dispersion. The maximum oxygen mass transfer coefficientis approximately 7 h^–1. A regime analysisindicated that there are mass transfer limitations in this type ofphotobioreactor. A methodology is described to determine the mass transfercoefficients for O₂ stripping and CO₂ dissolution whichwould be required to achieve a desired biomass productivity. This procedure canassist in determining design modifications to achieve the desired mass transfercoefficient.