Cephalosporin C production in a stirred tank reactor

Summary Cephalosporin C was produced with the moldCephalosporium acremonium in a 20 1 stirred tank reactor with 100 kg/m³ peanut flour in fed-batch operation. The growth and product formation was followed by on-line analysis of the broth composition. The cell concentration was estimated from the RNA-content of the cells. By optimization of the fed-batch operation and by increasing the phosphate content in the broth, a final cephalosporin C concentration of 12 kg/m³ was attained.Nomenclature CPC cephalosphorin C - DAC deacetylcephalosporin C - DAOC deacetoxycephalosporin C - k _L a volumetric mass transfer coefficient - MMBS 2-Hydroxy-4-methylmercaptobutyric acid - PABAH p-Hydroxybenzoicacidhydrazid - RNA ribonucleic acid - RQ respiratory quotient - oxygen transfer rate - CO₂-production rate - t fermentation time     

Interactions of cell morphology and transport processes in the lovastatin fermentation

The cholesterol lowering drug, Lovastatin (Mevacor), acts as an inhibitor of HMGCoA reductase, and is produced from an Aspergillus terreus fermentation.Pilot scale studies were carried out in 800 liter fermenters to determine the effects of cell morphology on the oxygen transport properties of this fermentation. Specifically, parallel fermentations giving (i) filamentous mycelial cells, and (ii) discrete mycelial pellets, were quantitatively characterized in terms of broth viscosity, availability of dissolved oxygen, oxygen uptake rates and the oxygen transfer coefficient under identical operating conditions.The growth phase of the fermentation, was operated using a cascade control strategy which automatically changed the agitation speed with the goal of maintaining dissolved oxygen at 50% saturation. Subsequently stepwise changes were made in agitation speed and aeration rate to evaluate the response of the mass transfer parameters (DO, OUR, and k _L a). The results of these experiments indicate considerable potential advantages to the pellet morphology from the standpoint of oxygen transport processes.List of Symbols DO % sat. Dissolved oxygen concentration - k _L a h^–1 Gas-liquid mass transfer coefficient - OUR mmol/dm³h Oxygen uptake rate - P/V KW/m³ Agitator power per unit volume - V _s m/s Superficial air velocity - _app cP Apparent viscosity     

A mathematical model for solid state fermentation in tray bioreactors

A simple mathematical model for the interaction of mass transport with biochemical reaction in solid state fermentations (SSF) in static tray type bioreactors under isothermal conditions has been developed. The analysis has enabled scientific explanations to a number of practical observations, through the concept of critical substrate bed thickness. The model will be most useful in the prediction of the concentration gradients as also in efficient design of these bioreactors.List of Symbols C g/cm³ Oxygen concentration in the bed - C _g g/cm³ Atmospheric oxygen concentration - C ^* Dimensionless oxygen concentration, C/C _g - D _e cm²/h Effective diffusivity - H cm Bed thickness or height - H _c cm Critical bed thickness or height - H _m cm Maximum height of zone of zero oxygen concentration - p _i mg/(g · h) Productivity (Eq. 13) - R g/(cm³ · h) Biochemical reaction rate - t h Fermentation time - t ^* Dimensionless time, D _e t/H² - X mg/cm³ Biomass concentration - X _max mg/cm³ Maximum biomass concentration - y Dimensionless thickness or height, (y = z/H) - y cm Thickness of zone of zero oxygen concentration (Eq. 12) - Y Yield coefficient - z cm Bed thickness or height along tray axis - Bed void fraction - _max h^–1 Specific growth rate - Thiele modulus      

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     

An energy cost minimizing strategy for fermentation dissolved oxygen control

A cost-minimizing mathematical model for on-line control of dissolved oxygen using agitation speed and aeration rate was developed. In pilot scale monensin fermentation using Streptomyces cinnamonensis, this algortihm provided stable control of dissolved oxygen at 40%, reducing energy usage 27.8%. The agitation and aeration profiles provided by the algorithm respresent the pathway of least energy cost for control at the desired dissolved oxygen level. Other observed advantages of bivariable control were reduction of foaming, evaporation, and gas holdup. Reduced maintenance of compressors and agitator motors could also be expected due to decreased load. Monensin productivity equivalent to fermentation with constant agitation and aeration was not obtained, however, with potency reduced 14.8% with the dissolved oxygen control strategy.List of Symbols A m² cross sectional area of fermentor - A ₁, A ₂, A ₃, A ₄ constants of polynomial fit to Calderbank's equations - BP N/m² gauge back pressure - C _ag $/W/s cost of electrical power - C _Q $/m³ cost of compressed air - CE mol/m³/s carbon dioxide evolution rate - D m impeller diameter - DO, DO _meas, DO _sp % dissolved oxyen saturation at any time, measured, and setpoint respectively - h m height of liquid in fermentor - H N/m²/mmol Henry's constant for oxygen in water - H _av average gas holdup in fermentor - k _L a, k _L a _meas, k _L k _sp s^–1 oxygen mass transfer coefficient at any time, measured, and setpoint respectively - N, N _sp s^–1 agitation speed at any time and setpoint respectively - N _a, N _{a, sp} aeration number at any time and setpoint respectively - N _i total number of impellers - N _p impeller power number - N _s number of impellers into which air is directly sparged - OU, OU _meas mol/m³/s Oxygen uptake rate at any time and measured respectively - P W ungassed agitation power - P _g, P _g,meas, P _g,sp W gassed agitation power at any time, measured, and set point respectively - Q, Q _meas, Q _sp m³/s aeration rate at any time, measured, and setpoint respectively - T K fermentation temperature - u _g m/s linear gas velocity - V m³ fermentation liquid volume - mole fraction of oxygen in fermentation off-gas - calculation constant - motor efficiency - $/s sum of agitation and aeration costs - kg/m³ liquid density     

Reactor comparison and scale-up for the microaerobic production of 2,3-butanediol by Enterobacter aerogenes at constant oxygen transfer rate

Stirred tank (STR), bubble column (BCR) and airlift (ALR) bioreactors of 0.05 and 1.5 m³ total volume were compared for the production of 2,3-butanediol using Enterobacter aerogenes under microaerobic conditions. Batch fermentations were carried out at constant oxygen transfer rate (OTR=35 mmol/lh). At 0.05 m³ scale, the STR reactor achieved much higher biomass and product concentrations than the BCR and ALR reactors. At 1.5 m³ scale, however, exactly the same biomass and product concentrations could be obtained in both STR and ALR reactors. The 1.5 m³ ALR reactor performed also much better than its counterpart at small scale, achieving a productivity 2.4-fold as high as that of the 0.05 m³ BCL and ALR reactors. No differences in performances were observed between BCR and ALR. As compared to STR the tower reactors have a 12 time higher energetic efficiency (referred to product formation) and thus should be the choice for large scale production of 2,3-butanediol.The criterion of constant OTR or constant k _L a is not applicable for the scale-up of this oxygen-sensitive culture due to strong influence of reactor hydrodynamics under microaerobic conditions. The effects of mixing and circulation time on growth and metabolism of E. aerogenes were quantitatively studied in scaled-down experiments with continuous culture. For a successful scale-up of this microaerobic culture it is necessary to have an homogeneous oxygen supply over the entire reactor volume. Under conditions of inhomogeneous oxygen supply an optimum liquid circulation time exists which gives a maximum production of 2,3-butanediol.List of Symbols BD 2,3-butanediol - [mmol/l] saturation value of dissolved oxygen - D [h^–1] dilution rate - D [mm] reactor diameter - D _K [mm] top section diameter - D _R [mm] stirrer diameter - D _S [mm] draft tube diameter - EtOH ethanol - E _P [kg/kWh] energy efficiency refered to product formation - H [mm] height of reactor - HAc acetate - H _L [mm] height of liquid - k _L a [h^–1] volumetric oxygen transfer coefficient - N [rpm=min^–1] stirrer speed - OTR [mmol/lh] oxygen transfer rate - OUR [mmol/lh] oxygen uptake rate - p [Pa] pressure - P [kW] power input - P/V _L [kW/m³] specific power input - [mmHg] oxygen partial pressure (mmHg) or - [mmol/l] dissolved oxygen (mmol/l) - [mmol/gh] specific oxygen uptake rate - q _P [mmol/gh] specific productivity - R [Nm/kgK] gas constant, R = 287.06 - RQ respiration quotient - t _c [s] liquid circulation time - T [°C or K] temperature - TCA tricarboxylic acid - u _G [cm/s] mean superficial gas velocity - v _G [m/s] gas velocity at nozzels of gas distributor - V_G [l/h] aeration rate at inlet - V [m³ or l] total volume - V _L [m³ or l] liquid volume - V _N [l/mol] gas mole volume under normal conditions, V _N = 24.4116 - X [g/l] biomass concentration - CO₂ mole fraction in the effluent gas - O₂ mole fraction in the effluent gas - inlet (above the gas distributor) - ratio of oxygen consumed through TCA cycle to the total oxygen uptake rate - [g/l or kg/m³] density - [%] degree homogeneity - outlet of fermenter or top of the dispersion phase Dedicated to the 65th birthday of Professor Fritz Wagner.We thank Dr. C. Posten and T. Gabel for support with the computer control system UBICON. T.-G. Byun gratefully acknowledges financial support by DAAD.     

Oxygen controlled batch cultivations of Schizophyllum commune for enhanced production of branched β-1,3-glucans

Oxygen and shear stress are the key factors for enhanced glucan production with Schizophyllum commune. During batch cultivation control of or (specific oxygen uptake rate) was achieved by variation of the impeller speed. Biomass was modelled by using the carbon and oxygen balance derived from exhaust data. At mycel growth a of 0.042 h^–1 presents just the border before oxygen limitation arises and is simultaneously the optimum operation condition for maximum glucan formation. Related to an overall cultivation time of 72 h a maximum of both productivity (4.3 kg m^–3 d^–1) and yield (13 kg m^–3) were obtained.List of Symbols C kg m^–3 concentration - k _L a h ^–1 volume related oxygen transfer coefficient - K _s mol m^–3 substrate saturation constant - N rpm impeller speed - % oxygen partial pressure of the liquid phase - kg m^–3h^–1 oxygen uptake rate - h^–1 specific oxygen uptake rate, kg O₂ (kg biomass h)^–1 - t h time - yield coefficient (biomass formed/oxygen consumed) Greek Symbols h^–1 specific growth rate Indices O ₂ oxygen - X biomass - L liquid phase - * gas/liquid interface - S substrate (glucose) Dedicated to the 65th birthday of Professor Fritz Wagner.This work was kindly supported in parts by B. Braun Biotech International. The authors are grateful to Prof. Dr. Fritz Wagner for scientific support and appreciate the technical assistance of Detlev Rasch     

Influence de la température sur la cinétique,de croissance et le coefficient de maintenance de Candida lipolytica cultivé sur n-alcane

The effect of growth temperature on the evolution of kinetic parameters and yields was determined for Candida lipolytica cultures with ntetradecane as substrate, in a temperature range of 18°C to 30°C, which is below the critical growth temperature in order to work only in the activation zone of these parameters.In such a culture limited by substrate transfer, growth rate depends on biological rates, related to microorganisms characteristics, and diffusional rates, related to mass transfer. The effect of temperature thus depends on the limiting step. The activation energy, calculated from exponential growth rate determinations is .When the activation energy is calculated from the maximal rate of cell production (determined at the growth curve's inflexion point), it's found to be E _X=71,200 J/mole in the 18°C–24°C range, and E _X=28,000 J/mole in the 24°C–30°C range. The latter one is characteristic of a diffusion-limited process. Above 24°C, growth is controlled by substrate-transfer, as physiological potentialities are preferentially increased with temperature than diffusional ones: 24°C is thus the transition temperature T _t from physiological to diffusional limitation.The apparent yield is almost constant, over the 18°C to 30°C temperature range, although maintenance coefficients are very dependent on temperature. The activation energies related to maintenance coefficients for alkane and oxygen respectively are and .The m _s/m_{O 2} ratio is about 3 (g/g), whereas that, for a strict oxidation reaction of n-tetradecane ought to be 3.47 (g/g). A satisfactory correlation, relating maintenance coefficients to the maximal growth rate of yeast, is given.

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Liste des symboles A constante de saturation de modèle de croissance(1) - B vitesse spécifique considérée - C substrat carboné ou oxygène (g/l) - E energie d'activation (J/mole) - S _m quantité de substrat consommée par maintenance au cours d'une fermentation discontinue (g) - O₂ quantité d'oxygène transférée au milieu de culture (g/l) - R rendement global de la fermentation - R rendement global de la fermentation - constante des gaz parfaits (J/mole K) - S concentration en substrat carboné (g/l) - T température de croissance (°K) - X concentration en biomasse (g/l) - Y rendement limite - m coefficient de maintenance (h^-1) - t duree de fermentation (h) - tømpérature de croissance (^o Celsius) - taux de croissance (h^-1) Indices 1 relatif à la température 1. - 2 relatif à la température 2 - c relatif au substrat carboné ou à l'oxygène - f relatif au temps final - i relatif au point d'inflexion - m maximum - mO₂ relatif au coefficient de maintenance sur l'oxygène - m _s relatif au coefficient de maintenance sur le substrat carboné - o relatif au temps initial - O₂ relatif à l'oxygène - s relatif au substrat carboné - t de transition - T relatif à la température de croissance T - U _m relatif au taux de croissance maximal - X relatif à la productivité maximale en biomasse     

The utilization of metabolic inhibitors for shifting product formation from xylitol to ethanol in pentose fermentations using Candida tropicalis

Summary Xylose, glucose and xylose/glucose mixtures were fermented with Candida tropicalis ATCC 32113 under aerobic, oxygen limited and anaerobic conditions. Ethanol yields were highest under oxygen limited conditions with xylose and xylose/glucose. Anaerobic conditions were best for glucose fermentations.The effect of four metabolic inhibitors (azide, carbonyl cyanide m-chlorophenyl hydrazone (CCCP), oligomycin A and valinomycin-K⁺) were then studied under oxygen limited conditions. Only azide had a significant influence on ethanol production. At 2¢10^-4 M concentrations, ethanol yield increased up to two times and xylitol levels were repressed by 90% for xylose and glucose/xylose fermentations. 4.2×10^-3 M azide gave highest ethanol yields in glucose fermentations. At this concentration of azide, however, cell growth was inhibited, which seemed to prevent ethanol production in xylose fermentations. The effect of azide is discussed in terms of fine-tuning the respiratory activity necessary for metabolism.     

The effect of dissolved oxygen tension and the utility of oxygen uptake rate in insect cell culture

Dissolved oxygen tension and oxygen uptake rate are critical parameters in animal cell culture. However, only scarce information of such variables is available for insect cell culture. In this work, the effect of dissolved oxygen tension (DOT) and the utility of on-line oxygen uptake rate (OUR) measurements in monitoring Spodoptera frugiperda (Sf9) cultures were determined. Sf9 cells were grown at constant dissolved oxygen tensions in the range of 0 to 30%. Sf9 metabolism was affected only at DOT below 10%, as no significant differences on specific growth rate, cell concentration, amino acid consumption/production nor carbohydrates consumption rates were found at DOT between 10 and 30%. The specific growth rate and specific oxygen uptake rate followed typical Monod kinetics with respect to DOT. The calculated _max and max were 0.033 h^-1 and 3.82×10^-10 mole cell^-1h^-1, respectively, and the corresponding saturation constants were 1.91 and 1.57%, respectively. In all aerated cultures, lactate was consumed only after glucose and fructose had been exhausted. The yield of lactate increased with decreasing DOT. It is proposed, that an apparent DOT in non-instrumented cultures can be inferred from the lactate yield of bioreactors as a function of DOT. Such a concept, can be a useful and important tool for determining the average dissolved oxygen tension in non-instrumented cultures. It was shown that the dynamic behavior of OUR can be correlated with monosaccharide (fructose and glucose) depletion and viable cell concentration. Accordingly, OUR can have two important applications in insect cell culture: for on-line estimation of viable cells, and as a possible feed-back control variable in automatic strategies of nutrient addition.Abbreviations DOT Dissolved oxygen tension - OUR Oxygen uptake rate - specific oxygen uptake rate - specific growth rate - X_v viable cell concentration - C_L, C^*, and oxygen concentrations in liquid phase, in equilibrium with gas phase, and medium molar concentration, respectively - H Henry's constant - K_La volumetric oxygen transfer coefficient - P_T total pressure - oxygen partial pressure - oxygen molar fraction - i discrete element     

On-line parameter and state estimation of continuous cultivation by extended Kalman filter

Summary The on-line estimation of biomass concentration and of three variable parameters of the non-linear model of continuous cultivation by an extended Kalman filter is demonstrated. Yeast growth in aerobic conditions on an ethanol substrate is represented by an unstructured non-linear stochastic t-variant dynamic model. The filter algorithm uses easily accessible data concerning the input substrate concentration, its concentration in the fermentor and dilution rate, and estimates the biomass concentration, maximum specific growth rate, saturation constant and substrate yield coefficient. The microorganismCandida utilis, strain Vratimov, was cultivated on the ethanol substrate. The filter results obtained with the real data from one cultivation experiment are presented. The practical possibility of using this method for on-line estimation of biomass concentration, which is difficult to measure, is discussed.Nomenclature D dilution rate (h^-1) - DO₂ dissolved oxygen concentration (%) - E identity matrix - F Jacobi matrix of the deterministic part of the system equations g - g continuousn-vector non-linear real function - h m-vector non-linear real function - K Kalman filter gain matrix - K _S saturation constant (kgm^-3) - K_S expectation of the saturation constant estimate - M Jacobi matrix of the deterministic part of the measurement equations h - P(t₀) co-variance matrix of the initial values of the state - P(t_k/t_k) c-variance matrix of the error in (t _k|t _k) - P(t_k+1/t_k) co-variance matrix of the error in (t _k+1|t _k - Q co-variance matrix of the state noise - R co-variance matrix of the output noise - S substrate concentration (kgm^-3) - S _i input substrate concentration - t time - t _k discrete time instant with indexk=0, 1, 2,... - u(t) input vector - v(t_k) measurement (output) noise sequence - w(t) n-vector white Gaussian random process - x(t₀) initial state of the system - (t₀) expectation of the initial state values - x(t) n-dimensional state vector - x(t_k) state vector at the time instantt _k - (t_k|t_k) expectation of the state estimate at timet _k when measurements are known to the timet _k - (t_k+1|t_k) expectation of the state prediction - X biomass concentration (kgm^-3) - expectation of the biomass concentration estimate - y(t_k) m-dimensional output vector at the time instantt _k - Y _XIS substrate yield coefficient - _X|S expectation of the substrate yield coefficient estimate - specific growth rate (h^-1) - _M maximum specific growth rate (h^-1) - expectation of the maximum specific growth rate estimate - state transition matrix     

Influence of hyperbaric oxygen tension on the metabolism of Candida tropicalis and Rhodococcus erythropolis

Summary The effect on metabolism of hyperbaric dissolved oxygen tension in batch cultures of Candida tropicalis (Cast.) Berkhout and Rhodococcus erythropolis with three different carbon sources was studied in a 20-l bioreactor under controlled conditions. The respiratory quotient was not significantly influenced by dissolved oxygen concentrations up to 40 mg/l oxygen. Elementary cell composition and proportional contents of DNA, RNA, and protein were not markedly influenced by the various oxygen concentrations but depended mainly on the growth rate. It was found that the production of trehalose lipid by R. erythropolis was dependent on the growth rate which could be enhanced by raising the oxygen concentration. The specific activity of catalase was affected more by the nature of the carbon source than by increased oxygen concentration. On the basis of the experimental data the application of oxygen-enriched air for biotechnological processes is discussed.Symbols and abbreviations k_La Specific volumetric oxygen transfer rate - Oxygen consumption rate, grams oxygen per hour and per liter - Carbon dioxide production rate, grams carbon dioxide per hour and per liter - RQ Respiratory quotient, - t Cultivation time - Y_X/S Yield coefficient, grams cell dry weight/grams substrate - Yield coefficient, grams cell dry weight/grams oxygen consumed - Y_kJ Yield coefficient, grams cell dry weight/heat of combustion of the consumed substrate - Y_ave– Yield coefficient, grams cell dry weight/mol available electrons of the consumed substrate     

Simplified typing of mouse hemoglobin (Hbb) phenotypes using cystamine

Cellulose acetate electrophoresis of mouse hemoglobins modified with the disulfide reagent cystamine permits rapid, unequivocal discrimination of all combinations of the codominant mouse hemoglobin single (Hbb ^s ) and diffuse (Hbb ^d and Hbb ^p ) alleles. The single, diffuse major, diffuse d-minor, and diffuse p-minor adult hemoglobins are all resolved by this method, which depends on the presence of a cysteine in the chains of diffuse mice which is not found in the chain of single mice.This work was supported by research grants ACS-VC58 and NIH CA-01074. The Jackson Laboratory is fully accredited by the American Association for Accreditation of Laboratory Animal Care.     

Effect of hydromechanical forces on the production of filamentous haemagglutinin and pertussis toxin ofBordetella pertussis

Summary The production ofBordetella pertussis extracytoplasmic filamentous haemagglutinin (FHA) and pertussis toxin (PT) in a bioreactor under stirring conditions was studied in order to investigate the effect of hydromechanical forces on yields of both antigens. It was shown that FHA loses its haemagglutinin activity when the power transmitted by the agitator and the aerator per unit volume increases, whereas PT production is not affected. The loss of FHA activity can be explained by the action of shear forces on the filamentous structure of this antigen.Nomenclature C^* dissolved oxygen saturation concentration - C₁ dissolved oxygen concentration - D impeller diameter - power transmitted by the agitator and the aerator per unit of liquid volume - E_m maximum local energy dissipation rate per unit of liquid volume - K_La volumetric oxygen transfer coefficient - N impeller speed - Pg power input in aerated system - qO₂m maximum specific oxygen consumption rate - R_e Reynold number (D²N /) - VVM volume of air per volume of fermentation broth per minute - Xm maximum of biomass concentration - o Kolmogorov-microscale - fermentation broth viscosity - fermentation broth kinematic viscosity - fermentation broth density - expt experiment     

Growth simulation ofHansenula polymorpha

Summary Using the model presented in part I, the measured time and spacial variations of process variables were simulated with satisfactory accuracy. Especially the experimentally found minima of the longitudinal dissolved oxygen concentration profiles in the substrate limiting growth range, which are caused by the transition from oxygen transfer limited to substrate limited growth along the tower, can be simulated with great accuracy.Symbols L length - M mass - T time - K temperature - M_M mole mass - a Specific gas/liquid interfacial area with regard to the liquid volume in the tower (L^–1) - DS_R Substrate feed rate (ML^–3T^–1) - K_O Saturation constant of Monod kinetics with regard to oxygen (ML^–3) - K_S Saturation constant of Monod kinetics with regard to the substrate (ML^–3) - K_ST Constant - K_L Mass transfer coefficient (LT^–1) - k_La Volumetric mass transfer coefficient (T^–1) - k_La^E Volumetric mass transfer coefficient at the entrance (T^–1) - k_La Volumetric mass transfer coefficient at large distances from the entrance (T^–1) - k_La ₀ Volumetric mass transfer coefficient in the absence of substrate (ethanol) (T^–1) - L_R Gas-liquid layer height in the tower (L) - L_R Height of the loop (L) - - O_B Dissolved oxygen concentration in the loop liquid (ML^–3) - O_F Dissolved oxygen concentration in the tower liquid (ML^–3) - O _F ^* Saturation value of O_F (ML^–3) - OTR Oxygen transfer rate (ML^–3T^–1) - P Pressure - Oxygen transfer rate (ML^–3T) - S_B Substrate concentration in the loop liquid (ML^–3) - S_D Substrate concentration at which k_La=2 k_La ₀ (ML^–3) - S_F Substrate concentration in the tower liquid (ML^–3) - T Absolute temperature - t Time (T) - u_Go Superficial gas velocity in the tower - V_R Reactor volume (L³) - V_G Volumetric gas flow rate in the tower (L³T^–1) - V_B Volumetric liquid flow rate in the loop (L³T^–1) - V_F Volumetric liquid flow rate in the tower (L³T^–3) - V_u Liquid recycling rate (L³T^–1) - X_B Biomass concentration in the loop liquid (ML^–3) - X_F Biomass concentration in the tower liquid (ML^–3) - x Longitudinal coordinate in the tower (L) - x^* Longitudinal coordinate in the loop (L) - x_OG O₂ mole fraction in the gas phase - Y_X/O Yield coefficient of biomass with regard to oxygen - Y_X/S Yield coefficient of biomass with regard to substrate - z=x/L_R Dimensionless longitudinal coordinate in the tower - z^*=x^*/L_B Dimensionless longitudinal coordinate in the loop - Constant (L_R is the distance from the aerator on which k_L a is space dependent) - Liquid recirculation ratio - _G Mean relative gas holdup in the tower - _exp Experimentally determined (T^–1) - _max Maximum specific growth rate (T^–1) - _F Liquid density (ML^–3) - A At the exit - E At the inlet     

Estimation of specific growth rate from agitation speed in DO-stat culture

Summary A simple and effective method to estimate the specific growth rate estimation has been developed based on the observation of time changes in the agitation speed in dissolved oxygen(DO)-stat cultures of Brevibacterium ketoglutamicum. The estimation was compared with that using carbon dioxide evolution rate (CER). Estimated values of specific growth rates by both methods agreed well with the data directly calculated from cell concentration change although the use of agitation speed gave a slightly better result than CER.Nomenclature CER Carbon dioxide evolution rate (mmol/sec) - OUR Oxygen uptake rate (mmol/sec) - OTR Oxygen transfer rate (mmol/sec) - RPM Agitation speed (rev./min) - C* Saturated dissolved oxygen concentration (mmol/L) - Dissolved oxygen concentration (mmol/L) - k Time index - k _L a' Mass transfer coefficient (sec^-1) - Y _X/O2 Cellular yield based on oxygen consumed (g-cell/mmol O₂) - Specific growth rate (hr^-1) - Constant - t Fermentation time - t Sampling time for RPM and CER measurements     

Induction effect of PO 2 during continuous yeast production from ethanol in a multistage tower fermentor

Summary The effect of the periodic variation of the partial pressure of oxygen in the aeration gas on biomass concentrations, ethanol conversion, yield and productivity during continuous cultivations of the yeast Candida utilis in a multistage tower fermentor was studied. The results were compared with those obtained under aeration conditions with a constant P_{O 2} in the aeration gas. The results demonstrated that, with the optimum P_{O 2} in the aeration gas, the aeration procedure with the periodic variation of P_{O 2} in the gas phase permitted achievement of the same process parameters as those under constant P_{O 2}. Using this new aeration procedure, the consumption of pure oxygen can be lowered by 55% to 60%. In addition, the significance of the induction effect of P_{O 2} on growth characteristics in the individual stages of the fermentor was proved.Symbols Ac Concentration of acetic acid (g/l) - i Number of stage - P_{O 2} Partial pressure of oxygen in the aeration gas (torr) - P_R Productivity of the fermentor (g cell dwt/l/h) - S_R Ethanol concentration in the feed (g/l) - S Ethanol concentration in the cultivation broth (g/l) - t Time of continuous cultivation (h) - X Cell dry weight concentration (g/l) - (Y_X/S)_W Yield of cell dry weight from ethanol for the whole fermentor (g cell dwt/g ethanol) - Concentration interval in which parameters varied during the long-term cultivation at constant constant P_{O 2}=263.5 torr in the aeration gas - ₁ Concentration interval in which parameters varied during the long-term cultivation before the increase of P_{O 2} in the aeration gas - ₂ Concentration interval in which parameters varied during the long-term cultivation immediately after the decrtease of P_{O 2} in the aeration gas - ₃ Concentration interval in which parameters varied during the long-term cultivation about 24 h after the decrease of P_{O 2} in the aeration gas - ₄ Concentration interval in which parameters varied during the long-term cultivation about 48 h after the decrease of P_{O 2} in the aeration gas     

Thermodynamic compensation in microbial thermal death

Sixty eight Arrhenius plots of thermal death in six mesophilic yeast species, tested at various concentrations of NaCl, lacked an isokinetic temperature. Nevertheless the H ^#/S ^# plot was apparently linear with a slope corresponding to 314° K. It was concluded that linear thermodynamic compensation of thermal death is non-existent in heterogeneous groups of yeasts and is unlikely to occur in heterogeneous groups of other organisms and that H ^#/S ^# plots lack sensitivity for the detection of non-linearity over narrow temperature ranges.However, the H ^# and S ^# parameters of thermal death displayed non-linear compensation in such a way that the extrapolated Arrhenius plots of death attained nearly identical values near the respective maximum temperatures for growth.Linear thermodynamic compensation occurred in each of the six strains, when stationary populations of the same strain were tested at various NaCl concentrations. On the other hand, exponential populations of each of the strains, tested in the same way, lacked an isokinetic temperature of thermal death.The significance of linear and non-linear thermodynamic compensation in biological rate processes is discussed.     

Carbon dioxide desorption from fermentation broth by use of oxygen vectors

The ability of oxygen vector to extract produced carbon dioxide has been tested in an anaerobic fermentation. During the continuous culture of Clostridium acetobutylicum at pH 4.6 and at a dilution rate of 0.124 h^–1, a feed composed of an emulsion of 18.5% by volume of Forane F66E was able to extract about 9% of the total CO₂ produced under CO₂ partial pressure equal to 0.42 atm. A theoretical evaluation of the extracted amount, based on the hypothesis of total saturation of the vector by carbon dioxide, has lead to very good agreement.List of Symbols [AA] g/l acetic acid concentration - [BA] g/l butyric acid concentration - D 1/h Q _w /V dilution rate - [ETH] g/l ethanol concentration - H _w Henry constant of CO₂ for water at 37°C (=23.91 mmol/(l atm)) - H _F Henry constant of CO₂ for Forane at 37°C (=83.4 mmol/(l atm)) - H _i g/mol molar mass of componenti - P _i atm partial pressure of gasi - W _w l/h aqueous flow - Q_f 1/h Forane flow - mmol/(lh) dissolved CO₂ flow in aqueous effluent - mmol/(lh) CO₂ gas flow - mmol/(lh) CO₂ gas flow without Forane - mmol/(lh) CO₂ gas flow with Forane - mmol/(lh) total CO₂ production - r _X g/(lh) biomass production rate - r _G mmol/(lh) total gas flow - mmol/(lh) hydrogen production - mmol/(lh) nitrogen flow - r _S mmol/(lh) glucose input - V 1 fermentor volume     

Estimation of oxygen penetration depth in immobilized cells

Summary A simple method is proposed for calculating oxygen pentration depth in immobilized cells by assuming zero order kinetics in the presence of several external oxygen transport resistances. Calculations indicate that typical penetration depths of oxygen for immobilized microbial cells are in the range of 50–200 and those for immobilized or encapsulated animal and plant tissue culture are about 500–1000 . Based on calculations, oxygen transport in microencapsulation and microcarriers for tissue cultures are not transport-limited, but a slight limitation is expected for those in a hollow fiber reactor.Nomenclature a_s specific area of a support (cm) - Bi Biot number - dimensionless - C_b oxygen concentration in the bulk liquid (mM) - C _b C _b ^* -C_cr (mM) - C _b ^* bulk oxygen concentration in equilibrium with air (mM) - C_cr critical oxygen concentration (mM) - C_s oxygen concentration in the solid phase (mM) - d_p diameter or thickness of a support (cm) - D_eff effective diffusivity of oxygen in the solid phase (cm²/s) - k_m membrane permeability of oxygen (cm/s) - k _m ^* D_eff/_m - k_La_L liquid phase mass transfer rate coefficient (1/s) - k_sa_s solid phase mass transfer rate coefficient (1/s) - (OUR)_v volumetric oxygen uptake rate (mmol O₂/l) - p geometry parameter, p=0 for slab, p=1 for cylinder, p=2 for sphere - P_d oxygen penetration depth (cm) - P _d oxygen penetration depth in the absence of external diffusion limitation (cm) - Q volumetric oxygen uptake rate, (mmol O₂/l·h) - specific oxygen uptake rate (mmol O₂gm biomass (dry)·h) - r length coordinate (cm) - r_c oxygen penetration depth for sphere (cm) - r _c r_c in the absence of external diffusion limitation (cm) - r _c ^* oxygen penetration depth for cylinder (cm) - r _c ^* r _c ^* in the absence of external diffusion limitation (cm) - r_com combined mass transfer rate resistance (s) - r_d location where C_s becomes zero or C_cr (cm) - r_i radius of cylinder or sphere, half thickness of slab (cm) - U_sg superficial gas velocity (cm/s) - X cell concentration (g/l) Greek letters Thiele modulus, dimensionless - _L, _s liquid and solid phase volume fraction, respectively, dimensionless - effectiveness factor On sabbatical leave from KAIST, Seoul, Korea