Gas-liquid mass transfer in bioreactor with three-phase inverse fluidized bed

In the present study the oxygen mass transfer from the gas to the aqueous phase in a Three-Phase Inverse Fluidized Bed (TPIFB) has been studied. A pilot scale TPIFB has been designed and constructed. For determination of the volumetric oxygen mass transfer coefficient the elegant dynamic method, described by Dang et al. (1977) was used. The influence of hydrodynamic parameters, e.g., superficial velocities of the gas and liquid phases on the mass transfer rate was studied. In the range of variables covered, it was found that the superficial liquid velocity had a weak effect on the mass transfer whereas the gas flowrate affects the mass transfer positively. The results for the volumetric oxygen transfer coefficient in the TPIFB were compared to reported values of that coefficient, measured in a classic three-phase fluidised bed under similar hydrodynamic conditions and solid phase properties. The comparison demonstrated a two-fold increase of the oxygen transfer rate in the inverse bed over that in the classic one.     

Mathematical description of bikaverin production in a fluidized bed bioreactor

Summary  Growth of Gibberella fujikuroi in submerged cultures occurs as micelles or filamentous hyphae dispersed in fluid and pellets or stable, spherical agglomerations. Gibberella fujikuroi growth, substrate consumption and bikaverin production kinetics obtained from submerged batch fermentation were fitted to three different sigmoid models: two and three-parameter Gompertz models and one Logistic model. Growth fitting was used to compare between models and select the best one by means of an F test. The best model for describing growth was the two-parameter Gompertz model and was used for glucose consumption and bikaverin production fitting. Data from eight different schemes of fermentations were analysed and parameter estimation was carried out by means of minimization of residual sum of squares. Some characteristic values obtained with the two-parameter Gompertz model fit are: μ=0.028 h⁻¹, Y_x/s=0.1089 g substrate/g biomass, α =0.1384 g product/g biomass.     

Production of ethanol by solid particles of Saccharomyces cerevisiae in a fluidized bed

Summary Carbon dioxide can be used as the fluid continuous phase for the fermentation of 10 to 40 % aqueous solutions of glucose into ethanol with Saccharomyces cerevisiae using a closed circuit consisting of a fluidized bed of small solid yeast particles, a cooled condenser for the sampling of water and ethanol and a blower. At 18°C, a fermentation of 12 moles glucose per min per g dry weight of yeast was achieved.     

Xylitol production by immobilized recombinant Saccharomyces cerevisiae in a continuous packed-bed bioreactor

Continuous xylitol production with two different immobilized recombinant Saccharomyces cerevisiae strains (H475 and S641), expressing low and high xylose reductase (XR) activities, was investigated in a lab-scale packed-bed bioreactor. The effect of hydraulic residence time (HRT; 1.3-11.3 h), substrate/cosubstrate ratio (0.5 and 1), recycling ratio (0, 5, and 10), and aeration (anaerobic and oxygen limited conditions) were studied. The cells were immobilized by gel entrapment using Ca-alginate as support and the beads were treated with Al(3+) to improve their mechanical strength. Xylose was converted to xylitol using glucose as cosubstrate for regeneration of NAD(P)H required in xylitol formation and for generation of maintenance energy. The stability of the recombinant strains after 15 days of continuous operation was evaluated by XR activity and plasmid retention analyses. Under anaerobic conditions the volumetric xylitol productivity increased with decreasing HRT with both strains. With a recycling ratio of 10, volumetric productivities as high as 3.44 and 5.80 g/L . h were obtained with the low XR strain at HRT 1.3 h and with the high XR strain at HRT 2.6 h, respectively. However, the highest overall xylitol yields on xylose and on cosubstrate were reached at higher HRTs. Lowering the xylose/cosubstrate ratio from 1 to 0.5 increased the overall yield of xylitol on xylose, but the productivity and the xylitol yield on cosubstrate decreased. Under oxygen limited conditions the effect of the recycling ratio on production parameters was masked by other factors, such as an accumulation of free cells in the bioreactor and severe genetic instability of the high XR strain. Under anaerobic conditions the instability was less severe, causing a decrease in XR activity from 0.15 to 0.10 and from 3.18 to 1.49 U/mg with the low and high XR strains, respectively. At the end of the fermentation, the fraction of plasmid bearing cells in the beads was close to 100% for the low XR strain; however, it was significantly lower for the high XR strain, particularly for cells from the interior of the beads. (c) 1996 John Wiley & Sons, Inc.     

Ethanol production in a hollow fiber bioreactor using Saccharomyces cerevisiae

Summary A new approach for continuous production of ethanol was developed using a Hollow fiber fermentor (HFF). Saccharomyces cerevisiae cells were packed into the shell-side of a hollow fiber module. Using 100 g/l glucose in the feed gave an optimum ethanol productivity, based on total HFF volume, of 40 g ethanol/l/h at a dilution rate of 3.0 h^-1. Under these conditions, glucose utilization was 30%. However, at 85% glucose utilization the productivity was 10 g ethanol/l/h. This compares to batch fermentor productivity of 2.1 g ethanol/l/h at 100% glucose utilization.     

Evaluation of production of recombinant human interleukin-2 in fluidized bed bioreactor

The production of recombinant human interleukin-2 in a fluidized bed bioreactor containing porous glass carriers is described. Cultivations were carried out with different medium formulations over 80 days. Maximal cell densities and product yield could be maintained even when protein free medium was perfused, with less than 10% cell washout. Due to this effective immobilization of the cells in the reactor, continuous operation was easy to perform. Final cell densities on the order of 3.8 x 10(8) mL(-1) intrasphere volume were reached while the interleukin-2 production rate was 0.75 mg L(-1) d(-1). The production rate showed a maximum of a 1.9 fold decrease compared with a homogeneous stirred bubble-free aerated system. This result was in contrast to that achieved with hybridoma cell lines, where better performance was obtained with the fluidized bed bioreactor. The situation may reflect the problems caused by the dense cell culture with adherent cells, as previously shown in a hollow-fiber bioreactor with the same cell line.     

Isopropanol biodegradation by immobilized Paracoccus denitrificans in a three-phase fluidized bed reactor

A three-phase bed bioreactor including a mix of immobilized microbes was used to degrade isopropanol (IPA). The immobilization method was studied and cells immobilized with calcium alginate, polyvinyl alcohol, activated carbon, and SiO₂ were demonstrated to be the best immobilization method for the degradation of 90% of 2?g/L IPA in just 4 days, 1 day earlier than with free cells. Acetone was monitored as an indicator of microbial IPA utilization as the major intermediate of aerobic IPA biodegradation. The bioreactor was operated at hydraulic retention time (HRT) values of 32, 24, 16, 12, and 10?hr, which correspond to membrane fluxes of 0.03, 0.04, 0.06, 0.08, and 0.10?L/m²/hr, respectively. The chemical oxygen demand (COD) removal efficiencies were maintained at 98.0, 97.8, 89.1, 80.6, and 71.1% at a HRT of 32, 24, 16, 12, and 10?hr, respectively, while the IPA degradations were 98.6, 98.3, 90.3, 81.6, and 73.3%, respectively. With a comprehensive consideration of COD removal and economy, the optimal HRT was 24?hr. The results demonstrate the potential of immobilized mixed bacterial consortium in a three-phase fluidized bed reactor system for the aerobic treatment of wastewater containing IPA.     

Ethanol fermentation in a magnetically fluidized bed reactor with immobilized Saccharomyces cerevisiae in magnetic particles

Ethanol fermentation by immobilized Saccharomyces cerevisiae cells in magnetic particles was successfully carried out in a magnetically stabilized fluidized bed reactor (MSFBR). These immobilized magnetic particles solidified in a 2 % CaCl(2) solution were stable and had high ethanol fermentation activity. The performance of ethanol fermentation of glucose in the MSFBR was affected by initial particle loading rate, feed sugar concentration and dilution rate. The ethanol theoretical yield, productivity and concentration reached 95.3%, 26.7 g/L h and 66 g/L, respectively, at a particle loading rate of 41% and a feed dilution rate of 0.4 h(-1) with a glucose concentration of 150 g/L when the magnetic field intensity was kept in the range of 85-120 Oe. In order to use this developed MSFBR system for ethanol production from cheap raw materials, cane molasses was used as the main fermentation substrate for continuous ethanol fermentation with the immobilized S. cerevisiae cells in the reactor system. Molasses gave comparative ethanol productivity in comparison with glucose in the MSFBR, and the higher ethanol production was observed in the MSFBR than in a fluidized bed reactor (FBR) without a magnetic field.     

Phenol degradation in a three-phase biofilm fluidized sand bed reactor

A previous three phase fluidized sand bed reactor design was improved by adding a draft tube to improve fluidization and submerged effluent tubes for sand separation. The changes had little influence on the oxygen transfer coefficients(K _L a), but greatly reduced the aeration rate required for sand suspension. The resulting 12.5 dm³ reactor was operated with 1 h liquid residence time, 10.2dm³/min aeration rate, and 1.7–2.3 kg sand (0.25–0.35 mm diameter) for the degradation of phenol as sole carbon source. The K _La of 0.015 s^–1 gave more than adequate oxygen transfer to support rates of 180g phenol/h · m³ and 216 g oxygen/h · m³. The biomass-sand ratios of 20–35 mg volatiles/g gave estimated biomass concentrations of 3–6 g volatiles/dm³. Offline kinetic measurements showed weak inhibition kinetics with constants ofK _s=0.2 mg phenol/dm³, K _o2=0.5 mg oxygen/dm³ and KinI= 122.5 mg phenol/dm³. Very small biofilm diffusion effects were observed. Dynamic experiments demonstrated rapid response of dissolved oxygen to phenol changes below the inhibition level. Experimentally simulated continuous stagewise operation required three stages, each with 1 h residence time, for complete degradation of 300 mg phenol/dm³ · h.     

Kinetics and thermodynamics of ethanol production by a thermotolerant mutant of Saccharomyces cerevisiae in a microprocessor-controlled bioreactor

AIMS: The present investigation deals with the development of thermotolerant mutant strain of yeast for studying enhanced productivity of ethanol from molasses in a fully controlled bioreactor. METHODS AND RESULTS: The parental culture of Saccharomyces cerevisiae ATCC 26602 was mutated using UV treatment. A single thermotolerant mutant was isolated after extensive screening and optimization, and grown on molasses medium in liquid cultures. The mutant was 1.45-fold improved than its wild parent with respect to ethanol productivity (7.2 g l-1 h-1), product yield (0.44 g ethanol g-1 substrate utilized) and specific ethanol yield (19.0 g ethanol g-1 cells). The improved ethanol productivity was directly correlated with titres of intracellular and extracellular invertase activities. The mutant supported higher volumetric and product yield of ethanol, significantly (P相似文献   

Use of a tapered fluidized bed as a Continuous bioreactor

Reactor systems based on tapered fluidized beds are being developed for aqueous bioprocesses in which adhering microorganisms or immobilized active biological fractions are used. The use of a fluidized bed prevents biomass buildup, accommodates particulates in the feed stream, is compatible with gas sparging, and allows easy removal or addition of the active materials. The tapered reactor tends to stabilize the fluidized bed, thus allowing a much wider range of operating conditions. Preliminary experimental results and an empirical mathematical model of the tapered bed indicate that bed stability is associated with a decreasing velocity and void-fraction profile up the bed and the pressure drop across the bed decreases with increasing flow rates. The tapered fluidized bed bioreactor is being evaluated for use in the enzymatic production of hydrogen, microbiological denitrification, and microbiological degradation of coal conversion aqueous waste streams. The enzyme catalyzed conversion of lactose to glucose and galactose was used in the evaluation of the reactor concept.     

Heterogeneous biofilm activity in a segregated anaerobic fluidized bed bioreactor

Bed segregation in a fluidized bed bioreactor profoundly influenced biofilm thickness and microbial activities of the biofilm along the bed height. Bioparticles coated with a thin biofilm, observed at the bottom of the reactor, had a higher specific activity in propylene glycol and n-propanol degradation than in thick biofilms developed at the top of the reactor. Although no significant difference was observed in specific activity for propionate and acetate along the reactor flow axis, more total propionate and acetate conversion occurred in regions of thicker biofilm accumulation.     

Biodegradation of sodium benzoate by a Gram-negative consortium in a laboratory-scale fluidized bed bioreactor

Gram-negative bacteria with the potential to metabolize n-alkanes and cyclic hydrocarbons were isolated from local soils and identified using 16S rDNA sequence analysis. Three isolates (CS1CO, GL1CO, GCI1CO) were identified as strains of Pseudomonas (P.) aeruginosa and a further strain (DSS2) as P. putida. Isolates were co-cultured in a laboratory-scale fluidized bed biofilm bioreactor (FBBR) utilizing sodium benzoate as the sole carbon source, under two batch and/or one continuous growth conditions. Biofilm and planktonic bacterial growth dynamics were monitored by plate counts, and optical density measurements (230 nm) determined benzoate biodegradation. Overall higher attached and planktonic bacterial counts, and benzoate depletion, were determined under batch compared to continuous conditions, and the bioreactor performed better during the second batch phase when compared to the first batch phase. It thus appeared that both the planktonic and biofilm components of the system were necessary for the most successful sodium benzoate degradation in this system.     

Effect of amino acids on glutathione production by Saccharomyces cerevisiae

Summary The constituent amino acids of the glutathione (GSH) tripeptide chain, glutamate, cysteine and glycine, were investigated for positive effects on GSH production in shake-flask cultures of Saccharomyces cerevisiae with glucose as the carbon source. Cysteine was confirmed as the key amino acid for increasing the specific GSH production rate, g, but showed some growth inhibition, especially in the second growth phase (ethanol-assimilation phase). An intracellular cysteine delivery agent, thiazolidine, showed a similar pattern of increased GSH production and growth inhibition, but to a slightly lesser degree, compared with free cysteine. The initial cysteine concentration affected both the specific growth rate, µ, and g, up to about 5 mm for µ and about 2–3 mm for g. Results of the [³⁵S]cysteine-labelling experiments suggest a complicated role of cysteine in increasing GSH production and further investigation may be necessary. Offprint requests to: S. Shioya     

Fed-batch cultivation of Saccharomyces cerevisiae in a hyperbaric bioreactor

Fed-batch is the dominating mode of operation in high-cell-density cultures of Saccharomyces cerevisae in processes such as the production of baker's yeast and recombinant proteins, where the high oxygen demand of these cultures makes its supply an important and difficult task. The aim of this work was to study the use of hyperbaric air for oxygen mass transfer improvement on S. cerevisiae fed-batch cultivation. The effects of increased air pressure up to 1.5 MPa on cell behavior were investigated. The effects of oxygen and carbon dioxide were dissociated from the effects of total pressure by the use of pure oxygen and gas mixtures enriched with CO(2). Fed-batch experiments were performed in a stirred tank reactor with a 600 mL stainless steel vessel. An exponential feeding profile at dilution rates up to 0.1 h(-)(1) was used in order to ensure a subcritical flux of substrate and, consequently, to prevent ethanol formation due to glucose excess. The ethanol production observed at atmospheric pressure was reduced by the bioreactor pressurization up to 1.0 MPa. The maximum biomass yield, 0.5 g g(-)(1) (cell mass produced per mass of glucose consumed) was attained whenever pressure was increased gradually through time. This demonstrates the adaptive behavior of the cells to the hyperbaric conditions. This work proved that hyperbaric air up to 1.0 MPa (0.2 MPa of oxygen partial pressure) could be applied to S. cerevisiae cultivation under low glucose flux. Above that critical oxygen partial pressure value, i.e., for oxygen pressures of 0.32 and 0.5 MPa, a drastic cell growth inhibition and viability loss were observed. The increase of carbon dioxide partial pressure in the gas mixture up to 48 kPa slightly decreased the overall cell mass yield but had negligible effects on cell viability.     

Biodegradation of dichloromethane in waste water using a fluidized bed bioreactor

Summary Biological treatment of a synthetic waste water containing 120 mM dichloromethane (10.2g/l) was carried out under aerobic conditions using dichloromethane-degrading bacteria as an inoculum. The bacteria were adsorbed to support particles and grown in a fluidized bed bioreactor. Charcoal and sand particles were compared as support materials with regard to abrasion, the maximum degradation rate for dichloromethane and the stability of the biological activity in the system.The use of charcoal led to the incorporation of coal dust into the biomass and to an uncontrollable thickness of the biofilm. Therefore the system became unstable and the biological activity decreased. In contrast sand as support material was indifferent to abrasion and allowed biofilm thickness to be controlled. The dichloromethane degrading capacity of the bioreactor increased during the first 30 days. It reached a steady state level of 1.6 g CH₂Cl₂/lxh. Dichloromethane concentration in the effluent was <0.01 mM (<0.85 mg/l) and consequently the degradation efficiency better than 99.99%.     

Modelling a solid-state fluidized bed fermenter for Ethanol production with S. cerevisiae

A model is proposed to describe the performance of a new type of fermenter for ethanol production, the fluidized bed gas-solid fermenter, with respect to scaling-up effects. Based on the fact that in the fluid bed the substrate is not supplied continuously to each particle, two scale-up parameters are derived, circulation time τ and specific substrate supply Δm _G,P , which are shown to influence reactor efficiency significantly. The validity of the model is checked by comparing the calculated yield coefficients for ethanol, cell mass and carbon dioxide to the results of fermentation experiments performed under aerobic conditions in a laboratory-scale reactor and a semi-technical fermenter.     

Mathematical model for a three-phase fluidized bed biofilm reactor in wastewater treatment

A mathematical model for a three phase fluidized bed bioreactor (TFBBR) was proposed to describe oxygen utilization rate, biomass concentration and the removal efficiency of Chemical Oxygen Demand (COD) in wastewater treatment. The model consisted of the biofilm model to describe the oxygen uptake rate and the hydraulic model to describe flow characteristics to cause the oxygen distribution in the reactor. The biofilm model represented the oxygen uptake rate by individual bioparticle and the hydrodynamics of fluids presented an axial dispersion flow with back mixing in the liquid phase and a plug flow in the gas phase. The difference of settling velocity along the column height due to the distributions of size and number of bioparticle was considered. The proposed model was able to predict the biomass concentration and the dissolved oxygen concentration along the column height. The removal efficiency of COD was calculated based on the oxygen consumption amounts that were obtained from the dissolved oxygen concentration. The predicted oxygen concentration by the proposed model agreed reasonably well with experimental measurement in a TFBBR. The effects of various operating parameters on the oxygen concentration were simulated based on the proposed model. The media size and media density affected the performance of a TFBBR. The dissolved oxygen concentration was significantly affected by the superficial liquid velocity but the removal efficiency of COD was significantly affected by the superficial gas velocity. An erratum to this article can be found online at .