Comparison of oxygen mass transfer coefficient in simple and extractive fermentation systems

Aeration and agitation are important variables to ensure effective oxygen transfer rate during aerobic bioprocesses; therefore, the knowledge of the volumetric mass transfer coefficient (k_La) is required. In view of selecting the optimum oxygen requirements for extractive fermentation in aqueous two-phase system (ATPS), the k_La values in a typical ATPS medium were compared in this work with those in distilled water and in a simple fermentation medium, in the absence of biomass. Aeration and agitation were selected as the independent variables using a 2² full factorial design. Both variables showed statistically significant effects on k_La, and the highest values of this parameter in both media for simple fermentation (241 s⁻¹) and extractive fermentation with ATPS (70.3 s⁻¹) were observed at the highest levels of aeration (5 vvm) and agitation (1200 rpm). The k_La values were then used to establish mathematical correlations of this response as a function of the process variables. The exponents of the power number (N³D²) and superficial gas velocity (V_s) determined in distilled water (α = 0.39 and β = 0.47, respectively) were in reasonable agreement with the ones reported in the literature for several aqueous systems and close to those determined for a simple fermentation medium (α = 0.38 and β = 0.41). On the other hand, as expected by the increased viscosity in the presence of polyethylene glycol, their values were remarkably higher in a typical medium for extractive fermentation (α = 0.50 and β = 1.0). A reasonable agreement was found between the experimental data of k_La for the three selected systems and the values predicted by the theoretical models, under a wide range of operational conditions.     

Syngas fermentation to biofuel: Evaluation of carbon monoxide mass transfer coefficient (kLa) in different reactor configurations

Lignocellulosic biomass such as agri‐residues, agri‐processing by‐products, and energy crops do not compete with food and feed, and is considered to be the ideal renewable feedstocks for biofuel production. Gasification of biomass produces synthesis gas (syngas), a mixture primarily consisting of CO and H₂. The produced syngas can be converted to ethanol by anaerobic microbial catalysts especially acetogenic bacteria such as various clostridia species.One of the major drawbacks associated with syngas fermentation is the mass transfer limitation of these sparingly soluble gases in the aqueous phase. One way of addressing this issue is the improvement in reactor design to achieve a higher volumetric mass transfer coefficient (k_La). In this study, different reactor configurations such as a column diffuser, a 20‐μm bulb diffuser, gas sparger, gas sparger with mechanical mixing, air‐lift reactor combined with a 20‐μm bulb diffuser, air‐lift reactor combined with a single gas entry point, and a submerged composite hollow fiber membrane (CHFM) module were employed to examine the k_La values. The k_La values reported in this study ranged from 0.4 to 91.08 h^?1. The highest k_La of 91.08 h^?1 was obtained in the air‐lift reactor combined with a 20‐μm bulb diffuser, whereas the reactor with the CHFM showed the lowest k_La of 0.4 h^?1. By considering both the k_La value and the statistical significance of each configuration, the air‐lift reactor combined with a 20‐μm bulb diffuser was found to be the ideal reactor configuration for carbon monoxide mass transfer in an aqueous phase. © 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2011     

Dynamic modeling of immobilized cell reactor: application to ethanol fermentation

A mathematical model has been developed for the unsteady-state operation of an immobilized cell reactor. The substrate solution flows through a mixed-flow reactor in which cells immobilized in gel beads are retained. The substrate diffuses from the external surface of the gel beads to some internal location where reaction occurs. The product diffuses from the gel beads into liquid medium which flows out of the reactor. The model combines simultaneous diffusion and reaction, as well as cell growth, and it can predict how the rates of substrate consumption, product formation, and cell growth vary with time and with initial conditions. Ethanol fermentation was chosen as a representative reaction in the immobilized cell reactor, and numerical calculations were carried out. Excellent agreement was observed between model predictions and experimental data available in the literature.     

Improved method for the dynamic measurement of mass transfer coefficient for application to solid–substrate fermentation

A new method has been developed for the measurement of overall volumetric mass transfer coefficient (K_L a) in gas-liquid-solid systems. This method is based on the examination of gas phase dynamics in a three-phase contactor and consists of measuring continuously the response of the outlet gas composition to a step input change of CO₂ in the inlet gas stream. The advantages and limitations of the new method are presented and its sensitivity is discussed on the basis of model predictions. Preliminary results on the implementation of the CO₂ method are also reported. Experimental data obtained in a nonviscous electrolyte solution show that the proposed method compares favorably with the conventional dissolved oxygen technique, provided that a correction is made to take account of the difference in diffusivity of oxygen and carbon dioxide.     

Characteristics of sisomicin fermentation supplemented with MgSO4 in stirred and air lift fermentors

Summary Sisomicin fermentations were carried out in stirred and air lift fermentors, and various concentrations of MgSO₄ were supplemented to improve antibiotic yield. The highest antibiotic yield was obtained at 80 mM in an air lift fermentor due to effective liberation of intracellular sisomicin by MgSO₄. The presence of high concentrations of MgSO₄, along with shear stress due to strong agitation in the stirred fermentor, resulted in low values of cell activity, rheological parameter(n) and cell viability in the stirred fermentor, compared with the air lift fermentor. The better physiological states of cells grown in the air lift fermentor resulted in improved antibiotic yields.     

Scale-up and application of a cyclone reactor for fermentation processes

A cyclone reactor for microbial fermentation processes was developed with high oxygen transfer capabilities. Three geometrically similar cyclone reactors with 0.5?l, 2.5?l and 15?l liquid volume, respectively, were characterized with respect to oxygen mass transfer, mixing time and residence time distribution. Semi-empirically correlations for prediction of oxygen mass transfer and mixing times were identified for scale-up of cyclone reactors. A volumetric oxygen mass transfer coefficient k _L a of 1.0?s^?1 (available oxygen transfer rate with air: 29?kg?m^?3?h^?1) was achieved with the cyclone reactor at a volumetric power input of 40?kW?m^?3 and an aeration gas flow rate of 0.2?s^?1. Continuous methanol controlled production of formate dehydrogenase (FDH) with Candida boidinii in a 15?l cyclone reactor resulted in more than 100% improvement in dry cell mass concentration (64.5?g?l^?1) and in about 100% improvement in FDH space-time yield (300?U?l^?1?h^?1) compared to steady state results of a continuous stirred tank reactor.     

The optimization of L-lysine fermentation and a mass transfer model

The efficiency of L-lysine biosynthesis is essentially determined by the power input and aeration ratio in the stirred fermenter. A mass transfer model was developed by means of the results of lysine fermentations in four geometrically similar fermenters with working volumes of 10 1, 50 1, 100 1 and 2500 1 which allows the optimization of lysine fermentation from the energetical point of view. The usefullness of this k_La-model is demonstrated with an example where the power input for an unknown fermenter is calculated.     

Mass transfer in a rectangular air-lift reactor: effects of geometry and gas recirculation

The interrelationships between the three parts of the air lift reactor, the riser, the downcomer, and gas-liquid separator, were examined with relation to the overall mass transfer in the reactor. This involved studying the mass transfer of oxygen from the gas phase to the liquid phase for 20 different reactor geometries. Both one- and two-sparger systems were studied. It was demonstrated that the gas-liquid separator plays a major role in reactor behavior and must be considered in reactor design. It was found that the overall reactor mass transfer coefficient KLA could be correlated to the pneumatic power of gas input per total dispersion volume (P/VD) and to the true riser superficial gas velocity JGR for all experimental conditions examined. The KLA is directly related to the P/VD with an exponent of approximately 1. "Two-sparger" systems, where an auxiliary gas sparger is placed near the downcomer entrance, have higher ab solute values for KLA than single-sparger systems.     

On-line enzyme activity determination using the stopped-flow technique: application to laccase activity in pulp mill waste-water treatment

An automated system for on-line measurement of enzyme activity is proposed. The system uses a flow injection manifold in the stopped-flow mode to measure initial reaction rates. The time during which the flow is halted is selected in such a way as to optimise the enzyme/substrate ratio for the correct determination of activity values. The proposed system was used to determine the activity of laccase produced by the fungus Trametes versicolor immobilised on nylon in a fixed-bed reactor used for treating pulp mill waste water. Received: 17 February 1997 / Received revision: 23 April 1997 / Accepted: 27 April 1997     

Growth of E. coli in a stirred tank and in an air lift tower reactor with an outer loop

E. coli ATCC 11105 was cultivated in a 10-1 stirred tank reactor and in a 60-1 tower loop reactor in batch and continuous operation. By on-line measurements of O₂ and CO₂ concentrations in the outlet gas, pH, temperature, cell mass concentration X as well as dissolved O₂ concentration along the tower in the broth, gas holdup, broth recirculation rate through the loop and by offline measurements of substrate concentration DOC and cell mass concentration along the tower, the maximum specific growth rate _m , yield coefficients Y _X/S. Y _X/DOC and were evaluated in stirred tank and tower loop in batch and continuous cultures with and without motionless mixers in the tower and at different broth circulation rates through the loop. To control the accuracy of the measurements the C balance was calculated and 95% of the C content was covered.The biological parameters determined depend on the mode of operation as well as on the reactor used. Furthermore, they depend on the recirculation rate of the broth and built-ins in the tower. The unstructured cell and reactor models are unable to explain these differences. Obviously, structured cell and reactor models are needed. The cell mass concentration can be determined on line by NADH fluorescence in balanced growth, if the model parameters are determined under the same operational conditions in the same reactor.List of Symbols a, b empirical parameters in Eq. (1) - CPR kg/(m³ h) CO₂ production rate - C kg/m³ concentration - D l/h dilution rate - DOC kg/m³ dissolved organic carbon - I net. fluorescence intensity - K _S kg/m³ Monod constant - k _L a l/h volumetric mass transfer coefficient - OTR kg/(m³ h) oxygen transfer rate - OUR kg/(m³ h) oxygen utilization rate - RQ = CPR/OUR respiratory quotient - S kg/m³ substrate concentration - t h,min, s time - t _u min recirculation time - t _M min mixing time - v m³/h volumetric flow rate through the loop - X kg/m³ (dry) cell mass concentration - Y _X/S yield coefficient of cell mass with regard to the consumed substrate - Y _X/DOC yield coefficient of the cell mass with regard to the consumed DOC - Y _X/O yield coefficient of the cell mass with regard to the consumed oxygen - Z relative distance in the tower from the aerator with regard to the height of the aerated broth - l/h specific growth rate - _m l/h maximum specific growth rate Indices f feed - e outlet     

A bioactive foamed emulsion reactor for the treatment of benzene-contaminated air stream

An adapted bioactive foamed emulsion bioreactor for the treatment of benzene vapor has been developed. In this reactor, bed clogging was resolved by bioactive foam as a substitute of packing bed for interfacial contact of liquid to gaseous phase. The pollutant solubility has been increased using biocompatible organic phase in liquid phase and this reactor can be applied for higher inlet benzene concentration. Experimental results showed a benzene elimination capacity (EC) of 220 g m⁻³ h⁻¹ with removal efficiency (RE) of 85% for benzene inlet concentration of 1–1.2 g m⁻³ at 15 s gas residence time in bioreactor. Assessment of benzene concentration in liquid phase showed that a significant amount of transferred benzene mass has been biodegraded. By optimizing the operational parameters of bioreactor, continuous operation of bioreactor with high EC and RE was demonstrated. With respect to the results, this reactor has the potential to be applied instead of biofilter and biotrickling filters.     

Heat and mass transfer effects in static solid-substrate fermentations: design of fermentation chambers

An experimental device was constructed to allow nearly simultaneous measurements to be made on temperature and gas composition at different depths in a solid-substrate fermentation bed. The time-dependent values of temperature, mol % O(2) and mol % CO(2) were measured at five positions in beds 6.35 cm (2.5 in.) deep. With a tempeh fermentation (Rhiopus oligosporus growing on soybeans) the temperature gradient could be as steep as 3 degrees C/cm during active mold growth and concentration of CO(2) could reach 21 vol. % in the bottom layer.     

Modeling of heat and mass transfer for solid state fermentation process in tray bioreactor

A mathematical model is developed to simulate oxygen consumption, heat generation and cell growth in solid state fermentation (SSF). The fungal growth on the solid substrate particles results in the increase of the cell film thickness around the particles. The model incorporates this increase in the biofilm size which leads to decrease in the porosity of the substrate bed and diffusivity of oxygen in the bed. The model also takes into account the effect of steric hindrance limitations in SSF. The growth of cells around single particle and resulting expansion of biofilm around the particle is analyzed for simplified zero and first order oxygen consumption kinetics. Under conditions of zero order kinetics, the model predicts upper limit on cell density. The model simulations for packed bed of solid particles in tray bioreactor show distinct limitations on growth due to simultaneous heat and mass transport phenomena accompanying solid state fermentation process. The extent of limitation due to heat and/or mass transport phenomena is analyzed during different stages of fermentation. It is expected that the model will lead to better understanding of the transport processes in SSF, and therefore, will assist in optimal design of bioreactors for SSF.     

Distribution of mass transfer rate and wall shear stress behind simple rectangular stenosis in pulsating flow

The distributions of mass transfer rate and wall shear stress in sinusoidal laminar pulsating flow through a two-dimensional asymmetric stenosed channel have been studied experimentally and numerically. The distributions are measured by the electrochemical method. The measurement is conducted at a Reynolds number of about 150, a Schmidt number of about 1000, a nondimensional pulsating frequency of 3.40, and a nondimensional flow amplitude of 0.3. It is suggested that the deterioration of an arterial wall distal to stenosis may be greatly enhanced by fluid dynamic effects.     

Hydrodynamic and mass transfer characteristics of three-phase gaslift bioreactor systems.

This review focuses on the hydrodynamic and mass transfer characteristics of various three-phase, gaslift fluidized bioreactors. The factors affecting the mixing and volumetric mass transfer coefficient (k(L)a), such as liquid properties, solid particle properties, liquid circulation velocity, superficial gas velocity, bioreactor geometry, are reviewed and discussed. Measurement methods, modeling and empirical correlations are reviewed and compared. To the authors' knowledge, there is no 'generalized' correlation to calculate the volumetric mass transfer coefficient, instead, only 'type-specific' correlations are available in the literature. This is due to the difficulty in modeling the gaslift bioreactor, caused by the variation in geometry, fluid dynamics, and phase interactions. The most important design parameters reported in the literature are: gas hold-up, liquid circulation velocity, 'true' superficial gas velocity, mixing, shear rate, aeration rate and volumetric mass transfer coefficient, k(L)a.     

Mathematical analysis of two-phase mass transfer in a batch reactor for the chemical transformation of a steroid

A reactor is described for the conversion of the slightly water-soluble steroid testosterone (T) to 4-androstene-3, 17-dione (4-AD) by enzyme in the presence of excess cofactor. Since the enzyme is subject to substrate inhibition, reaction rates are strong functions of aqueous substrate concentration. High concentrations of the substrate, testosterone, per unit reactor volume are maintained within poly(dimethylsiloxane) beads that are suspended in the aqueous enzyme solution. Mass transfer (controlled by bead size, polymer to water volume ratio, enzyme loading) is used to control the degree and rate of conversion. The reactor dynamics are predicted over a wide range of reaction conditions. The product steroid is recovered in the polymeric beads from the enzyme solution.     

Application of UASB-reactors to industrial waste-water treatment; performance data and results in granulation control

Several types of high organic matter pollutants containing (COD-range: 3–50 kg · m^?3) industrial waste waters were treated in laboratory scale (1.2–23 dm³) sludge blanket (UASB) and UASB-fixed bed hybrid (UBF) reactors. In most cases higher than 80% of COD-removal efficiency has been attained. The CO₂ content of the biogas developed was mainly influenced by the neutralization (base to acid) ratio related to feed pH. Cell immobilization by granule formation was considered as a change in microbial population: enrichment and aggregate formation of Methanotrix-like filamentous microorganisms. Based on physiological and physical indexes of microbial selection and with regard to the different sensitivities of microorganisms to substrate inhibition, a new start-up method was developed for rapid (40–45 days) granulation of raw digested sludge.     

Applications of thin layer chromatography,high performance liquid chromatography and mass spectrometry in the fermentation and isolation of the antibiotic nybomycin

Summary Thin layer chromatography (TLC), high performance liquid chromatography (HPLC) and mass spectrometry (MS) methods have been developed for the analysis of the antibiotic nybomycin, its derivatives deoxynybomycin and nybomycin acetate, during the fermentation and isolation of nybomycin. Using a quantitative HPLC based assay, the time course of nybomycin production (nybomycin titers) in 1000 liter fermentations was determined. Desorption chemical ionization mass spectrometry (DCI/MS) of standard nybomycin samples, fermentation broth samples and purified fractions suggested the co-production of deoxynybomycin which was not reported previously from this organism. TLC and HPLC were used to confirm the presence of deoxynybomycin in the crude extracts of fermentation broths.     

Effects of solid-phase mass transfer on the performance of a stirred anaerobic sequencing batch reactor containing immobilized biomass

This work reports on experiments for an anaerobic sequencing batch reactor containing immobilized biomass which aimed at verifying the effects of solid-phase mass transfer on the reactor's overall performance. Four experiments were carried out at 30 degrees C with cubic polyurethane foam particles previously inoculated with anaerobic biomass. Different solid-phase mass transfer conditions were reached in each experiment by varying the size of the bioparticle from 0.5 to 3.0 cm. The reactor was fed with a low-strength synthetic wastewater containing protein, carbohydrates and lipid and the effects of mass transfer were evaluated through dynamic substrate concentration profiles during 8-hour batch cycles. A modified first-order kinetic model provided a good representation of the behavior of the dynamic concentration profiles. The solid-phase mass transfer was found to slightly affect the concentration of effluent organic matter expressed as chemical oxygen demand (COD). The concentration of residual effluent substrate increased as the size of the bioparticle was increased. The cycle time was not affected as the size of the bioparticle was increased from 0.5 to 2.0 cm. However, it was found that the cycle time in a reactor with 3.0-cm cubic particles should be higher than that required in systems with smaller particles. The apparent first-order kinetic parameter was estimated as 0.59+/-0.01 h(-1) for experiments with bioparticle sizes ranging from 0.5 to 2.0 cm, while a value of 0.48 h(-1) was obtained in the experiment with 3.0-cm bioparticles.