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1.
Gas holdup investigation was performed in two external-loop airlift bioreactors of laboratory (V L =1.189·10?3? 1.880·10?3 m3; H R =1.16 ? 1.56 m; H D = 1.10 m; A D /A R = 0.111 ? 1.000) and pilot scale (V L =0.157?0.170 m3; H R =4.3?4.7 m; H D =4.0?4.4 m;A D /A R =0.04?0.1225), respectively, using as liquid phase non-Newtonian starch solutions of different concentration with K=0.061?3.518 Pa sn and n=0.86?0.39 and fermentation broths of P. chrysogenum, S. griseus, S. erythreus, B. licheniformis and C. acremonium at different hours since inoculation and from different batches. The influence of bioreactor geometry, liquid properties and the amount of introduced compressed air was investigated. The effect of sparger design on gas holdup was found to be negligible. It was found that gas holdup depends on the flow media index, ?GR decreasing with the increase of liquid pseudoplasticity, A D /A R ratio and H R /H D ratio. The experimental data are in agreement with those presented in literature by Popovic and Robinson, which take into account liquid properties, geometric parameters and gas superficial velocity, with a maximum error of ±30%. It was obtained a correlation for gas holdup estimation taking into account the non-Newtonian behaviour of the fermentation broths and the dry weight of the solid phase, as well. The concordance between the experimental data and those calculated with the proposed correlation was good, with a maximum error of ±17%. Also, a dimensionless correlation for gas holdup involving superficial velocities of gas and liquid, cross sectional areas ratio, dispersion height to riser diameter ratio, as well as Froude and Morton numbers, was obtained. 相似文献
2.
In order to obtain further information on the behaviour and optimal design of external-circulation-loop airlift bioreactors, the liquid circulating velocity was studied using highly viscous pseudoplastic solutions of starch and antibiotic biosynthesis liquids of Penicillium chrysogenum, Streptomyces griseus, Streptomyces erythreus, Bacillus licheniformis and Cephalosporium acremonium. Measurements of liquid circulation velocity were made in laboratory and pilot plant external-loop airlift bioreactors, under various conditions concerning gas flow rate, riser liquid height at constant downcomer height, A D /A R ratio, using the impulse-response technique. It has been found that these parameters had a significant effect on liquid circulation velocity together with the apparent viscosity and dry weight of the solid phase in the biosynthesis liquids. For the tested liquids, the superficial liquid velocity in the riser section of an external-loop airlift bioreactor may be described by the following equation: where the exponents and the constant c take different values depending on the liquid phase properties and flow regime. 相似文献
3.
Liquid circulation velocity was studied in externalloop air-lift bioreactors of laboratory and pilot scale, respectively for different gas input rates, downcomer-to-riser cross-sectional area ratio, A
D/AR and liquid phase apparent viscosities.It was found that, up to a gas superficial velocity in the riser v
SGR 0.04 m/s the dependency of v
SLR on v
SGR is in the following form: v
SLR = a v
SGR
b
, with the exponent b being 0.40. Over this value of v
SGR, only a small increase in liquid superficial velocity, v
SLR is produced by an increase in v
SGR.
A
D/AR ratio affects the liquid superficial velocity due to the resistance in flow and overall friction.For non-Newtonian viscous liquids, the circulation liquid velocity in the riser section of the pilot external-loop airlift bioreactor is shown to be dependent mainly on the downcomer-to-riser cross-sectional area ratio, A
D/AR, the effective (apparent) liquid viscosity,
eff and the superficial gas velocity, v
SGR.The equation proposed by Popovic and Robinson [11] was fitted well, with an error of ± 20%.List of Symbols
A
D m2
downcomer cross-sectional area
-
A
Rm2
riser cross-sectional area
- a =
coefficient in Eq. (7)
-
b =
exponent in Eq. (7)
-
c
s m–1
Coefficient in Eq. (3)
-
D
D m
downcomer diameter
-
D
R m
riser diameter
-
g m2/s
gravitational acceleration
-
H
D m
dispersion height
-
H
L m
ungassed liquid height
-
K Pa s
n
consistency index
-
K
B =
friction factor at the bioreactor bottom
-
K
F =
friction factor
-
K
T =
friction factor at the bioreactor top
-
V
L m3
liquid volume in the bioreactor
-
V
D m3
liquid volume in downcomer
-
V
R m3
liquid volume in riser
-
v
LDm/s
downcomer linear liquid velocity
-
v
LR m/s
riser linear liquid velocity
-
v
SGR m/s
riser superficial liquid velocity
-
v
SLR m/s
riser superficial liquid velocity
-
s–1
shear rate
-
GD =
downcomer gas holdup
-
GR =
riser gas holdup
-
eff Pa s
effective (apparent) viscosity
-
Pa
shear stress
The authors wish to thank Mrs. Rodica Roman for the help in experimental data collection and to Dr. Stefanluca for the financial support. 相似文献
4.
H. Buchholz R. Buchholz H. Niebeschütz K. Schügerl 《Applied microbiology and biotechnology》1978,6(2):115-126
Summary Mean relative gas holdup, slip velocity, bubble size distribution, mean specific interfacial area, and volumetric mass transfer coefficient of oxygen were estimated in sparged columns 14 cm in diameter and 380 and/or 390 cm high with two different aerator types (porous plate and injector nozzle) in highly viscous Newtonian (glycerol solutions) and non-Newtonian (CMC solutions) fluids.For the Newtonian liquids the above properties were estimated as function of the viscosity of the liquid. For the non-Newtonian liquids they were determined as function of the fluid consistency index and flow behavior index. Significant differences between Newtonian and non-Newtonian systems appear. In Newtonian medium kL a drops with increasing viscosity and already approaches a constant value at =40 cP. In pseudoplastic medium kL a varies with the fluid consistency and flow behavior indexes in the entire investigated range.In both of these systems the primary bubble population changes into two or three populations along the reactor: the medium bubbles gradually disappear and small and large bubbles are formed. 相似文献
5.
The time-dependent gas hold-up is investigated during the aeration of the Saccharomyces cerevisiae suspension, the aqueous saccharose solutions and the glycerol solutions in the external loop airlift reactor. Due to the time-dependent bubble size distribution the fraction of the small bubble hold-up in the total gas hold-up decreases with an increase of the gas flow rate and with a decrease of the viscosity. The course of the accumulation process of the small bubbles is described by the first-order kinetic equation. The small bubble accumulation rate is investigated in the airlift reactor and the bubble column. It is showed that the small bubbles form and disappear exclusively in the riser of the airlift reactor. It is found that the small bubble-liquid mass transfer coefficient is several times larger than the overall oxygen transfer coefficient. 相似文献
6.
7.
8.
Effect of scale-up on average shear rates for aerated non-Newtonian liquids in external loop airlift reactors 总被引:1,自引:0,他引:1
Al-Masry WA 《Biotechnology and bioengineering》1999,62(4):494-498
Average shear rates have been estimated experimentally in a 700-dm3 external loop airlift reactor. Aqueous pseudoplastic carboxymethylcellulose and xanthan gum solutions were used to simulate non-Newtonian behavior of biological media. Average shear rates of non-Newtonian solutions were found by analogy with Newtonian glycerol solutions using downcomer liquid velocity as the measurable parameter. Due to the complexity of local shear rate measurement, an average shear rate was assumed to exist and is proportional to superficial gas velocity. The data from this work and those in the literature were used in producing a new correlation for estimating average shear rates as a function of superficial gas velocity, geometry, and dispersion height. Wall shear rates were found to be significant. The ratio of wall shear rates to bulk shear rates were varied from 5% to 40%. Furthermore, it has been found that shear rates generated in airlift loop reactors are lower than those generated in bubble columns. Copyright 1999 John Wiley & Sons, Inc. 相似文献
9.
10.
The paper presents a model of the motion of a particle subjected to several transport processes in connection with mixing in two phase flow. A residence time distribution technique coupled with a one-dimensional dispersion model was used to obtain the axial dispersion coefficient in the liquid phase, Dax. The proposed model of Dax for an external-loop airlift bioreactor is based on the stochastic analysis of the two-phase flow in a cocurrent bubble column and modified for the specific flow in the airlift reactor. The model takes into account the riser gas superficial velocity, the riser liquid superficial velocity, the Sauter bubble diameter, the riser gas hold-up, the downcomer-to-riser cross sectional area ratio. The proposed model can be applied with an average error of ᆨ. 相似文献
11.
The specific aspects of airlift reactors emphasizing their function relevance to particular application as bioreactors are presented. The two main groups of airlift reactors – external-loop and concentric-tube reactors – were investigated on a pilot-plant scale with regard to their performance during the cultivation of unicellular and filamentous microorganisms which produce Bacitracin, Cephalosporin C and Nystatin. Some results were compared to those obtained in conventional stirred tank bioreactors. The comparison was carried out based on physical properties (oxygen transfer rate (OTR), volumetric mass transfer coefficient (kLa) and efficiency of oxygen transfer (E)), cell mass, productivity and substrate consumption, secondary metabolite production, and efficiency of the product formation with regard to the specific power input. It was shown that B. licheniformis, C. acremonium and S. noursei fermentations occurred similarly to those performed in stirred vessels, proving that the capacity of the airlift bioreactors surpassed the problems which arise from the morphology and rheology of the broths. From the chemical engineering point of view, it was obvious that the primary tasks of a bioreactor (uniform distribution of microorganisms and nutrients over the entire fermenter volume, appropriate supply of biomass with nutrients and oxygen) were fulfilled by the airlift bioreactors tested. In addition, the efficiency of oxygen transfer (OTR referred to power input) in the airlift fermenters proved to be about 38% higher than in the stirred tank bioreactors (expressed as average values), while the sorption efficiency (OTR referred to antibiotic production) was found to be 22% greater in the airlift system than in an STR. Therefore, the biosyntheses were performed with about a 30–40% increase in energy efficiency and energy savings compared to the conventional system. Moreover, the lack of mechanical devices in the airlift system provides greater safety and a gentler environment for the cultivation of microorganisms. 相似文献
12.
Amelioration of ligninolytic enzyme production by Phanerochaete chrysosporium in airlift bioreactors 总被引:1,自引:0,他引:1
Maximum activities of manganese-dependent peroxidase (MnP) and lignin peroxidase (LiP) in free cultures of Phanerochaete chrysosporium (ATCC 24725) were 258 U l–1 and 103 U l–1, respectively, in an airlift bioreactor. Immobilisation of the fungus on an inert carrier as well as several design modifications of the bioreactor employed gave MnP activities around 500–600 U l–1 during 9 days' operation. The continuous operation of the latter led to MnP and LiP activities about 140 U l–1 and 100 U l–1, respectively, for two months, without operational problems. Furthermore, the extracellular liquid secreted decolourised the polymeric dye Poly R-478 about 56%. 相似文献
13.
Hydrodynamic behaviour of animal cell microcarrier suspensions in split-cylinder airlift bioreactors 总被引:3,自引:0,他引:3
Hydrodynamic characteristics of suspensions of microcarriers used for culturing anchorage dependent animal cells are reported in split-cylinder internal-loop airlift bioreactors. Cell culture media are simulated using salt solutions that duplicate the ionic strengths of typical media. Effects of solids loading (0–30 kg·m–3), microcarrier particle size (150–300×10–6 m diameter) and density (1030–1050 kg·m–3) on gas induced circulation of the slurry, mixing time, gas holdup and gas velocity requirements to attain complete suspension of solids are discussed for two reactors with aspect ratios of 7.6 and 14.5, but equal riser-to-downcomer cross-sectional area ratios of 1.0, aerated at low air flow rates (0–8×10–6 m3·s–1) through a sintered glass sparger with 110×10–6 m diameter pores. The study covers the ranges of solids concentrations, types, densities, particle sizes and aeration rates that are of relevance in animal cell culture applications.Airlift bioreactors displayed suitable hydrodynamic characteristics for potentially supporting anchorage dependent cell cultures on microcarriers at carrier loadings similar to those that are currently used in stirred tank bioreactors. The minimum gas flow rates and the induced liquid circulation rates necessary to achieve and maintain suspension of the heaviest and the largest microcarriers were well within practicable limits, limits which have been shown to be withstood by animal cells in non-anchorage dependent suspension culture in airlift bioreactors. No floatation problems were encountered with the carriers, nor was sedimentation a problem so long as the identified minimum suspension criteria were met. Chisti's liquid circulation equation, originally intended for two-phase flow, applied to the three-phase gas-liquid-microcarrier systems. 相似文献
14.
Forty- and ninety-liter airlift bioreactors have been used successfully to grow hybridoma cell lines in chemically defined serum-free media. In the airlift bioreactor, hybridoma cell growth and monoclonal antibody productivity are comparable to that obtained by conventional cell culture. At sparging rates of 0.60-1.20 vvh (volume of sparged gas per bioreactor volume per hour), the airlift bioreactor achieves rapid mixing and adequate oxygen mass transfer. Foaming is minimal and inconsequential for serum-free media and media supplemented with 5%-10% fetal bovine serum. The use of serum-free medium facilitates monoclonal antibody purification and enhances the purity of the final MAb product. 相似文献
15.
Suspension cultures of Berberis wilsonae produce 4 berberine-type alkaloids: berberine, palmatine, columbamine and jatrorrhizine. In particular the formation of the phenolic alkaloids columbamine and jatrorrhizine and of berberine proves to be dependent on the concentration of dissolved oxygen. With higher aeration rates, berberine and jatrorrhizine yields can be increased considerably. Thus we reached an alkaloid yield of more than 3 g × 1–1 with 50% dissolved oxygen tension in the medium. As far as we know this is one of the best results in fermenting of alkaloid-producing cell cultures.Abbreviations pO2
dissolved oxygen concentration in % saturation (using air)
- HPLC
high-performance liquid chromatography
- vvm
volume air × volume medium–1 × minute–1
- rpm
revolutions per minute
- IAA
indole-3-acetic acid
- 2,4-D
2,4-dichlorophenoxy acetic acid 相似文献
16.
The selection of the supports for biomass immobilisation is of great importance to obtain a stable biofilm leading to a high nitrification efficiency. In this work five type of supports were assayed in external loop air-lift reactors: sand, limestone, basalt, pumice and poraver. The efficiencies of the supports were compared and discussed in terms of their surface-properties: surface free energy of interaction, surface charge, porosity and shape. The results showed that materials leading to low surface free energies of interaction and with less negative surface charges favour bacterial adhesion and the formation of stable biofilms. High porosities are also relevant for bacterial colonisation. However, irregular shaped particles may promote the erosion of attached biomass. 相似文献
17.
B. Kawalec-Pietrenko 《Bioprocess and biosystems engineering》2000,23(4):397-402
Results of the investigations of the liquid circulation velocity in the external loop airlift reactor with the fluidized bed in the downcomer are reported. Densities of solid particles are much lower than the liquid density. It is found that the curve of the liquid circulation velocity dependence on the gas flow rate consists of two different parts. A slow linear increase of the liquid circulation velocity is observed if the gas velocity is lower than the minimum fluidization velocity. An exponential course of the liquid circulation velocity curve is observed if the gas flow rate exceeds the minimum fluidization velocity. A theoretical equation for the prediction of liquid circulation velocity for gas velocities higher than the minimum fluidization velocity is presented. 相似文献
18.
Hairy roots of red beet (Beta vulgaris L.) were cultivated in different types of airlift bioreactors (cone, balloon, bulb, drum and column bioreactors of 5 l capacity and containing 3 l of half strength Murashige & Skoog medium). The cone type of airlift bioreactor gave the highest biomass of hairy roots and betacyanin accumulation. Betacyanin accumulation was 27 mg g–1 dry wt in cultures aerated at 0.3 vvm. Light irradiation of 20 mol m–2 s–1 promoted hairy root growth but optimum betacyanin (34 mg g–1 dry wt) accumulation was with the cultures grown under 60 mol m–2 s–1. 相似文献
19.
20.
Lippert J Adler I Meyer HD Lübbert A Schügerl K 《Biotechnology and bioengineering》1983,25(2):437-450
During the cultivation of E. coli in an airlift tower-loop bioreactor, the following properties were measured: transverse profiles of Sauter bubble diameter, d(S); local relative gas holdup, E(G); bubble rise velocity, u(BS); local mean velocity, ū turbulence intensity, u'; macrotime scale, T(EL); dissipation time scale, tau(E); power spectrum, E(n); and energy dissipation spectrum D(n) at different distances from the aerator. The influence, distance from the aerator, absence and/or presnece of cells, and batch and/or continuous-culture operation on the behavior of the two-phase system are discussed on the basis of these properties. 相似文献