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Enhancement of oxygen mass transfer in stirred bioreactors using oxygen-vectors. 1. Simulated fermentation broths 总被引:4,自引:0,他引:4
Oxygen mass transfer represents the most important parameter involved in the design and operation of mixing-sparging equipment for bioreactors. It can be described and analyzed by means of the mass transfer coefficient, kLa. The kLa values are affected by many factors such as geometrical and operational characteristics of the vessels, media composition, type, concentration and microorganism morphology, and biocatalysts properties. The efficiency of oxygen transfer could be enhanced by adding oxygen-vectors in broths, such as hydrocarbons or fluorocarbons, without increasing the energy consumption for mixing or aeration. The experimental results obtained for simulated broths indicated a considerable increase of kLa in the presence of n-dodecane, and the existence of a certain value of n-dodecane concentration that corresponds to a maximum mass transfer rate of oxygen. The magnitude of the positive effect of n-dodecane depends both on the broths characteristics and operational conditions of the bioreactor.Notation d stirrer diameter, mm - d oxygen electrode diameter, mm - D bioreactor diameter, mm - h distance from the inferior stirrer to the bioreactor bottom, mm - H bioreactor height, mm - kLa oxygen mass transfer coefficient, s-1 - l impeller blade length, mm - I oxygen electrode immersed length, mm - P power consumption for mixing of non-aerated broths, W - Pa power consumption for mixing of aerated broths, W - (Pa/V) specific power input, W/m3 - s baffle width, mm - vS superficial air velocity, m/s - V volume of medium, m3 - w impeller blade height, mm - volumetric fraction of oxygen-vector - a apparent viscosity, Pa*s - density, kg/m3 相似文献
2.
Caşcaval D Galaction AI Turnea M 《Journal of industrial microbiology & biotechnology》2011,38(9):1449-1466
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
kl a = aCXb ( \fracPa V )g vSd , 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). 相似文献
3.
Galaction AI Kloetzer L Turnea M Webb C Vlysidis A Caşcaval D 《Journal of industrial microbiology & biotechnology》2012,39(6):877-888
This paper is dedicated to the study on external and internal mass transfers of glucose for succinic fermentation under substrate and product inhibitions using a bioreactor with a stationary basket bed of immobilized Actinobacillus succinogenes cells. By means of the substrate mass balance for a single particle of biocatalysts, considering the Jerusalimsky kinetic model including both inhibitory effects, specific mathematical expressions have been developed for describing the profiles of the substrate concentrations and mass flows in the outer and inner regions of biocatalyst particles, as well as for estimating the influence of internal diffusion on glucose consumption rate. The results indicated that very low values of internal mass flow could be reached in the particles center. The corresponding region was considered biologically inactive, with its extent varying from 0.24% to 44% from the overall volume of each biocatalyst. By immobilization of bacterial cells and use of a basket bed, the rate of glucose consumption is reduced up to 200 times compared with the succinic fermentation system containing free cells. 相似文献
4.
Galaction AI Cascaval D Turnea M Folescu E 《Bioprocess and biosystems engineering》2005,27(4):263-271
The previous works on simulated broths are continued and developed for Propionibacterium shermanii broths. The obtained results indicated the considerable increase of k
L
a in presence of n-dodecane as oxygen-vector and the existence of a certain value of hydrocarbon concentration that corresponds to the maximum
mass transfer rate of oxygen. The magnitude of the positive effect of the oxygen-vector strongly depends on operational conditions
of the bioreactor, on broth characteristics and on P. shermanii concentration. 相似文献
5.
Galaction AI Rotaru R Kloetzer L Vlysidis A Webb C Turnea M Caşcaval D 《Journal of microbiology and biotechnology》2011,21(12):1257-1263
This paper is dedicated to the study on the external and internal mass transfers of glucose for succinic acid fermentation under substrate and product inhibitions using a bioreactor with stirred bed of immobilized Actinobacillus succinogenes cells. By means of the substrate mass balance for a single particle of biocatalysts, considering the kinetic model adapted for both inhibitory effects, specific mathematical models were developed for describing the profiles of the substrate concentration in the outer and inner regions of biocatalysts and for estimating the substrate mass flows in the liquid boundary layer surrounding the particle and inside the particle. The values of the mass flows were significantly influenced by the internal diffusion velocity and rate of the biochemical reaction of substrate consumption. These cumulated influences led to the appearance of a biological inactive region near the particle center, its magnitude varying from 0 to 5.3% of the overall volume of particles. 相似文献
6.
Cascaval D Galaction AI Turnea M 《Journal of industrial microbiology & biotechnology》2007,34(1):35-47
The study on mixing distribution for an aerobic stirred bioreactor and simulated (solutions of carboxymethylcellulose sodium salt), yeasts (S. cerevisiae) and fungus (P. chrysogenum pellets and free mycelia) broths indicated the significant variation of mixing time on the bioreactor height. The experiments suggested the possibility to reach a uniform mixing in whole bulk of the real broths for a certain value of rotation speed or biomass concentration domain. For S. cerevisiae broths the optimum rotation speed increased to 500 rpm with the biomass accumulation from 40 to 150 g/l d.w. Irrespective of their morphology, for fungus cultures the existence of optimum rotation speed (500 rpm) has been recorded only for biomass concentration below 24 g/l d.w. The influence of aeration rate depends on the apparent viscosity/biomass concentration and on the impellers and sparger positions. By increasing the apparent viscosity for simulated broths, or biomass amount for real broths, the shape of the curves describing the mixing time variation is significantly changed for all the considered positions. The intensification of the aeration induced the increase of mixing time, which reached a maximum value, decreasing then, due to the flooding phenomena. This variation became more pronounced at higher viscosities for simulated broths, at higher yeasts concentration, and at lower pellets or filamentous fungus concentration, respectively. By means of the experimental data and using MATLAB software, some mathematical correlations for mixing time have been proposed for each broth and considered position inside the bioreactor. These equations offer a good agreement with the experiment, the maximum deviation being ±7.3% for S. cerevisiae broths. 相似文献
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