Ethanol production by immobilized whole cells ofZymomonas mobilis in a continuous flow expanded bed bioreactor and a continuous flow stirred tank bioreactor

Continuous ethanol fermentation by immobilized whole cells ofZymomonas mobilis was investigated in an expanded bed bioreactor and in a continuous stirred tank reactor at glucose concentrations of 100, 150 and 200 g L^–1. The effect of different dilution rates on ethanol production by immobilized whole cells ofZymomonas mobilis was studied in both reactors. The maximum ethanol productivity attained was 21 g L^–1 h^–1 at a dilution rate of 0.36 h^–1 with 150 g glucose L^–1 in the continuous expanded bed bioreactor. The conversion of glucose to ethanol was independent of the glucose concentration in both reactors.     

Feasibility of culturing C2C12 mouse myoblasts on glass microcarriers in a continuous stirred tank bioreactor

Commercial culturing of mammalian cell lines is increasing in importance as more biological products unique to mammals are being produced in genetically altered mammalian cells. Most mammalian cells are anchorage dependent, so they must be cultured on a support matrix. This limitation, along with the requirement of a low shear environment, severely effects the scale-up of bench-scale culture systems. The need to culture mammalian cells on a support matrix limits the increase in cell population to a factor of 10-20 before growth virtually stops due to contact inhibition. Commercial culturing systems for anchorage dependent cells are batch processes because of the combination of contact inhibition and support matrix requirements. Development of a continuous bioreactor system could allow both unlimited scale-up and continuous cell-mass production. To design a continuous reactor, a mathematical model to predict the reactor performance should be developed. This paper addresses the development of a mathematical model for predicting continuous bioreactor performance. It was found that anchorage dependent C2C12 mouse myoblast cells, a continuous cell line, followed Monod kinetics for glucose consumption and cell mass production in batch flask experiments, with w_max = 0.040 hr^у and K_m = 2.5 mM. Furthermore, it was found that these parameters could be used to predict the glucose consumption in a continuous bioreactor operated with constant feed of seeded microcarriers operated at two different residence times. The success of this model implies the possibility of developing a continuous cell harvesting and reinoculation system using a microcarrier bioreactor to produce cell mass.     

A cartridge oxygenator for mammalian cell culture in a stirred tank bioreactor

Summary Tubing made of membrane with high oxygen permeability is often used in supplying oxygen to animal cell culture bioreactors. We have fabricated the tubing into a cartridge configuration. Such an arrangement allows damaged tubing to be replaced conveniently and eases the maintenance of such an oxygenator in bioreactors.     

In situ filtration of Anchusa officinalis culture in a cell-retention stirred tank bioreactor

Summary The effect of agitation and aeration on filtration of Anchusa officinalis culture in a stirred tank bioreactor integrated with an internal filter unit was investigated. Increases in suction head of the pump that drove the filtration process were measured at impeller speeds of 100 and 200 rpm. Surprisingly, suction head attained at 200 rpm was about 40% higher than at 100 rpm. Direct observation of the cake deposition process in the reactor using a dilute cell suspension revealed that the filter cake formed at 100 rpm was thicker, but less compact. Aeration at 0.4 vvm was shown to have little effect on the filtration rate, since the bulk fluid flow was dominated by the impeller hydrodynamics. The initial flux can be recovered by filter backwashing with compressed air at a flow rate of 0.6 vvm for a duration of 5 minutes.     

Determination of the average shear rate in a stirred and aerated tank bioreactor

A method for evaluating the average shear rate () in a stirred and aerated tank bioreactor has been proposed for non-Newtonian fluids. The volumetric oxygen transfer coefficient (k _L a) was chosen as the appropriate characteristic parameter to evaluate the average shear rate (). The correlations for the average shear rate as a function of N and rheological properties of the fluid (K and n) were obtained for two airflow rate conditions (ϕ_air). The shear rate values estimated by the proposed methodology lay within the range of the values calculated by classical correlations. The proposed correlations were utilized to predict the during the Streptomyces clavuligerus cultivations carried out at 0.5 vvm and four different rotational impeller speeds. The results show that the values of the average shear rate () varied from 437 to 2,693 s⁻¹ by increasing with N and flow index (n) and decreasing with the fluid consistency index (K).     

An approximate solution for a transient two-phase stirred tank bioreactor with nonlinear kinetics

The derivation of an approximate solution method for models of a continuous stirred tank bioreactor where the reaction takes place in pellets suspended in a well-mixed fluid is presented. It is assumed that the reaction follows a Michaelis-Menten-type kinetics. Analytic solution of the differential equations is obtained by expanding the reaction rate expression at pellet surface concentration using Taylor series. The concept of a pellet's dead zone is incorporated; improving the predictions and avoiding negative values of the reagent concentration. The results include the concentration expressions obtained for (a) the steady state, (b) the transient case, imposing the quasi-steady-state assumption for the pellet equation, and (c) the complete solution of the approximate transient problem. The convenience of the approximate method is assessed by comparison of the predictions with the ones obtained from the numerical solution of the original problem. The differences are in general quite acceptable.     

Optimizing control of a continuous stirred tank fermenter using a neural network

Feedforward neural networks are a general class of nonlinear models that can be used advantageously to model dynamic processes. In this investigation, a neural network was used to model the dynamic behaviour of a continuous stirred tank fermenter in view of using this model for predictive control. In this system, the control setpoint is not known explicitly but it is calculated in such a way to optimize an objective criterion. The results presented show that neural networks can model very accurately the dynamics of a continuous stirred tank fermenter and, the neural model, when used recursively, can predict the state variables over a long prediction horizon with sufficient accuracy. In addition, neural networks can adapt rapidly to changes in fermentation dynamics.List of Symbols F Dimensionless flow rate (F/ V₀) - F m³/h Flow rate - F ₀ m³/h Inlet flow rate - J Objective cost function - K _i Dimensionless constant in Eq. (3) (k _i /s₀) - k _i kg/m³ Substrate inhibition constant in Haldane model - k _m Dimensionless constant in Eq. (3) (k _s /s₀) - k _m kg/m³ Substrate inhibition constant in Haldane model - n prediction horizon - S Dimensionless substrate concentration (s/s₀) - s kg/m³ Substrate concentration - t h Time - v Dimensionless volume (V/V₀) - V m³ Liquid volume in fermenter - W _ij , W _jk Weight matrices in neural network - X Dimensionless biomass concentration - x kg/m³ Biomass concentration - Y Biomass/substrate yield coefficient - Weighting factor in Eq. (4) - Dimensionless specific growth rate (/ ) - 1/h Maximum specific growth rate - 1/h Specific growth rate - Dimensionless time ( t)     

Scale-up of biotransformation process in stirred tank reactor using dual impeller bioreactor

The gas-liquid mass transfer coefficient K(L)a in the fermenter is a strong function of mode of energy dissipation and physico-chemical properties of the liquid media. A combination of disc turbine (DT) and pitched blade turbine down flow (PTD) impellers has been tested in laboratory bioreactor for gas hold-up and gas-liquid mass transfer performance for the growth and biotransformation medium for an yeast isolate VS1 capable of biotransforming benzaldehyde to L-phenyl acetyl carbinol (L-PAC) and compared with those in water.Correlations have been developed for the prediction of the fractional gas hold-up and gas-liquid mass transfer coefficient for the above media. The mass transfer coefficient and respiration rate have been determined in the shake flask for the growth as well as for biotransformation medium. These results, then have been used to optimize the operating parameters (impeller speed and aeration) for growth and biotransformation in a laboratory bioreactor. The comparison of cell mass production and L-PAC production in the bioreactor has been done with that obtained in shake flask studies.     

Transient behavior of a continuous stirred tank biological reactor utilizing phenol as an inhibitory substrate

Transient experiments were conducted on a Pseudomomas utilizing phenol in a continuous culture by disturbing the influent substrate concentration and dilution rate. Two stable steady states existed for some ranges of the parameters. Highly damped oscillations were observed in approaching a new high conversion steady state or in returning to a new high conversion steady state following a small disturbance. When a large disturbance was applied there was a smooth (overdamped) approach to a new low conversion steady state. The observed oscillatory behavior for small disturbances was predicted by a modified Powell-Ierusalemskii bottleneck model, but could not be predicted by a Monod-Haldane model; neither model was accurate for predicting the effect of large disturbances. A constant wall growth factor was used to account for microbial film activity, and the existence of two stable states was directly due to the presence of the film.     

Suspended aggregates as an immobilization mode for high-density perfusion culture of HEK 293 cells in a stirred tank bioreactor

Cells of the human embryonic kidney cell line (HEK 293) grown in repeated suspension and perfusion systems were characterized and described. Cell aggregates that formed immediately after the HEK 293 cells were inoculated in stirred vessels in serum-containing Dulbecco’s modified Eagle’s medium (D-MEM)/F-12 medium. The mean diameter of the cell aggregates reflecting the aggregate size increased with culture time, shifting from 63 to 239 μm after 1 and 8 days of culture in spinner flasks, respectively. No significant differences in cell performance were observed between HEK 293 cell populations grown as suspended aggregates and those grown as anchored monolayers. Replacing the D-MEM/F-12 with CD 293 medium caused the compact spherical cell aggregates to dissociate into single cells and small irregular aggregates without any apparent effect on cell performance. Moreover, the spherical cell aggregates could reform from individual cells and small aggregates when exposed to the serum-containing D-MEM/F-12 dominant medium. Perfusion culture of HEK 293 cells grown as suspended aggregates in a 7.5-l stirred tank bioreactor for 17 days resulted in a maximum viable cell density of 1.2×10⁷ cells ml⁻¹. These results demonstrate the feasibility and proof-of-concept for using aggregates as an immobilization system in large-scale stirred bioreactors because a small-scale culture can be used as easily as the inoculum for larger bioreactors.The first two authors contributed equally to this work.     

Consecutive immobilized enzymatic reactions in continuous stirred tank reactor systems

The performance characteristics of two-enzyme reaction in a continuous stirred tank reactor (CSTR) are analytical investigated in this work. A model is formulated to describe the substrate concentration variations by taking into account the external and internal diffusion resistances. It is found that the reaction system exhibits the characteristics of reaction control or diffusion control depending on the operating conditions. The single CSTR model is also extended to describe the multiple CSTR system. The latter model enables the prediction of the number of CSTRs in series required to achieve a prescribed substrate conversion.     

Operational stability of immobilized d-glucose isomerase in a continuous feed stirred tank reactor

d-Glucose isomerization has been studied using immobilized cells of Streptomyces phaeochromogenes in a continuous feed stirred tank reactor (CSTR) where the external film diffusion resistance was negligible. Experiments conducted with various sizes of enzyme particles indicated that a strong internal diffusion resistance improved the apparent stability of these particles. The performance equations of the CSTR were constructed by associating the material balances for the inside porous support matrix with the bulk liquid phase, and enzyme deactivation was also taken into consideration. An iterative method together with the orthogonal collocation method is proposed for the evaluation of effectiveness factor and the substrate concentration profile within the enzyme particles. The numerical results offer an alternative analytical proof for the observation that under strong internal diffusion control the apparent operational stability of immobilized enzyme is improved.     

Optimization and control of a continuous stirred tank fermenter using learning system

A variable structure learning automaton is used as an optimization and control of a continuous stirred tank fermenter. The algorithm requires no modelling of the process. The use of appropriate learning rules enables to locate the optimum dilution rate in order to maximize an objective cost function. It is shown that a hierarchical structure of automata can adapt to environmental changes and can also modify efficiently the domain of variation of the control variable in order to encompass the optimum value.List of Symbols f Random number - F Dimensionless flow rate (F/V ₀) - F m³/h Flow rate - F ₀ m³/h Inlet flow rate - J Objective function - K _i Dimensionless constant in Eq. (3) (k _i/s₀) - k _i · kg/m³ Substrate inhibition constant in Haldane model - K _m Dimensionless constant in equation (3) (k _s/s₀) - k _m kg/m³ Substrate inhibition constant in Haldane model - L Number of levels of the hierarchical system of automata - N Number of possible control actions - p Probability - S Dimensionless substrate concentration (s/s ₀) - s kg/m³ Substrate concentration - T Dimensionless sampling period - t h Time - v Dimensionless volume (V/V ₀) - V m³ Liquid volume in fermenter - W Input to the stochastic automaton - X Dimensionless biomass concentration - x kg/m³ Biomass concentration - Y Biomass/substrate yield coefficient - Weighting factor in Eq. (4) - Dimensionless specific growth rate (/ ^*) - ^* h^–1 Maximum specific growth rate - h^–1 Specific growth rate - Dimensionless time ( t)     

Combined effect of hydrodynamic and interfacial flow parameters on lysozyme deactivation in a stirred tank bioreactor

The dynamic environment within a bioreactor and in the purification equipment is known to affect the activity and yield of enzyme production. The present research focuses on the effect of hydrodynamic flow parameters (average energy dissipation rate, maximum energy dissipation rate, average shear rate, and average normal stress) and the interfacial flow parameters (specific interfacial area and mass transfer coefficient) on the activity of lysozyme. Flow parameters were estimated using CFD simulation based on the k-epsilon approach. Enzyme deactivation was investigated in 0.1, 0.3, 0.57, and 1 m i.d. vessels. Enzyme solution was subjected to hydrodynamic stress using various types of impellers and impeller combinations over a wide range of power consumption (0.03 < P(G)/V < 7, kW/m3). The effects of tank diameter, impeller diameter, blade width, blade angle, and the number of blades on the extent of deactivation were investigated. At equal value of P(G)/V, epsilon(max), and gamma(avg), the extent of deactivation was dramatically different for different impeller types. The extent of deactivation was found to correlate well with the average turbulent normal stress and the mass transfer coefficient.     

Disturbance-accommodating control approach applied for the control of a continuous stirred tank reactor

This paper describes an experimental study of linear adaptive control to achieve the monitoring of a continuous stirred tank reactor. The practical control objective was the regulation of the substrate concentration at a pre-specified value in the process effluent despite local changes and/or culture physiology variations. The substrate concentration and the dilution rate have been selected as the controlled and the control variable respectively. The results obtained confirm that this approach offers the possibility to combine simplicity and effectiveness in bioprocess control.     

Studies on the production of enantioselective nitrilase in a stirred tank bioreactor by Pseudomonas putida MTCC 5110

Nitrilases constitute an important class of hydrolases, having numerous industrial applications. The present work aims to address the production of nitrile hydrolyzing enzymes from Pseudomonas putida MTCC 5110 in a 6l bioreactor. Effect of various physico-chemical conditions and process parameters like pH, temperature, aeration and agitation rates and inducer concentration was studied. Further, the enzyme activity was enhanced by adopting the inducer feeding strategy. Various biochemical engineering parameters pertaining to the cultivation of P. putida in different physico-chemical conditions were reported. Finally, segregation of growth phase from the enzyme production phase allowed significant reduction in total fermentation time.     

Production of mouse embryoid bodies with hepatic differentiation potential by stirred tank bioreactor

Embryonic stem (ES) cells can differentiate into functional hepatic lineage cells, which can potentially be used in biomedicine. To obtain hepatic lineage cells from ES cells, embryoid bodies (EBs) must be formed. In this study, we developed an EB formation system using a spinner flask for mass production of EBs. ES cells were inoculated into the spinner flask, where they formed EBs within 4 d. The EBs were then transferred into an attached culture for hepatic differentiation. To verify the hepatic lineage cells, albumin secretion and hepatic-specific gene expression were examined. We found that EBs formed by either the spinner flask or hanging drops exhibited similar albumin secretion potential and hepatic-specific gene expression. We conclude that the spinner flask method can be used to produce mouse EBs that can be used to mass produce hepatic lineage cells for use in biomedicine.     

Hydrogen metabolic patterns driven by Clostridium-Streptococcus community shifts in a continuous stirred tank reactor

Applied Microbiology and Biotechnology - The hydrogen (H2) production efficiency in dark fermentation systems is strongly dependent on the occurrence of metabolic pathways derived from the...