I. J. Dunn

Transient‐state behavior of a biofilter removing mixtures of vapors of MEK and MIBK from air

In the work reported here, selected aspects of the dynamic behavior of biofilters for waste air treatment have been investigated. Emphasis was placed on transient state elimination of mixtures of methyl ethyl ketone (MEK) and methyl isobutyl ketone (MIBK) vapors and on explanation of the observed phenomena. The initial startup, the response of the biofilter to step changes in the pollutant loadings, responses to pollutant pulses, restarting after starvation, and the influence of step changes in gaseous phase oxygen partial pressure are presented and discussed.

Modeling of enzymatic reactions in vesicles: The case of α‐chymotrypsin

: The kinetic behavior of the alpha-chymotrypsin-catalyzed hydrolysis of the two p-nitroanilide substrates succinyl-L-Ala-L-Ala-L-Pro-L-Phe-p-nitroanilide (Suc-Ala-Ala-Pro-Phe-pNA) and benzoyl-L-Tyr-p-nitroanilide (Bz-Tyr-pNA) was modeled and simulated for two different systems, namely for an aqueous solution and for a vesicle system, which was composed of phospholipid vesicles containing entrapped alpha-chymotrypsin. In the case of the vesicles, the substrate was added to the bulk, exovesicular aqueous phase. The experimentally determined time-dependence of product (p-nitroaniline) formation was modeled by considering the kinetic behavior of the enzyme and-in the case of vesicles-the substrate permeability across the bilayer membrane. In aqueous solution-without vesicles-the kinetic constants kcat and KS (respectively KM) were determined from fitting the model to experimental data of batch product concentration-time curves. The results were in good agreement with the corresponding values obtained from initial velocity measurements. For the vesicle system, using the phospholipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), simulation showed that the substrate permeation across the bilayer was rate limiting. Using experimental data, we could obtain the substrate permeability coefficient for Bz-Tyr-pNA by parametric fitting as 2. 45 x 10(-7) cm/s.

The effect of imperfect mixing on an idealized kinetic fermentation model

Abstract Mixing patterns in stirred reactors are analyzed in this study from the point of view of the hysteresis behavior of final product rate as a function of the intermediate concentration in the sequential reaction A → B → C . A two-tank system model with an internal recycle stream is studied, in order to simulate the effect of imperfect mixing in a single batch reactor. The extent of mixing between positions at which product and intermediate species concentrations are measured in the reactor is revealed in both the direction of the hysteresis function and the relative magnitude of the inscribed area. Another approach, which apparently simplifies the analysis, is to measure the concentration of B in each of the two tanks and cross-plot the two variables. This latter technique not only avoids the errors resulting from differencing the data, but also leads to correlations between the circumscribed areas and the degree of mixing.

Design and characterization of a multistage, mechanically stirred column absorber

Abstract A multistage, mechanically stirred column absorber has been designed and built with a modular construction, based on preliminary experiments with a test column. The column has been characterized as a gas-liquid contactor by its gas holdup, gas and liquid axial dispersion, mixing times, oxygen transfer coefficients and power consumptions, determined as a function of gas velocity, liquid velocity and impeller speed for one and two impellers per stage. Gassed power was correlated with ungassed power, gas rate and impeller speed. The gas phase axial mixing was essentially plug flow and the liquid phase axial mixing varied between 5 and 12 equivalent stages. Oxygen transfer coefficients were correlated with power consumptions and aeration rates by the equation K L a γ (P/V) a (υ sg ) b . The oxygen transfer coefficients with single stiffer stages were 25% above those for the double stirrer stages for equal power consumption and gas rates. Except for the low aeration and high power consumption extremes, the column showed superior oxygen transfer performance. in comparison to tubular loop and tank fermenters.

ANALYSIS OF FED-BATCH MICROBIAL CULTURE

The semicontinuous operation of fermenters is applied industrially for the production of yeast and antibiotics, but only relatively recently has this procedure, known as fed-batch fermentation, been analyzed theoretically. References 1-1 5 provide a background to the previous theoretical and experimental work on fed-batch culture. The present paper summarizes and unifies material which appears in references 2, 5 and 10. In addition, the topic of fed-batch product productivity is extended.

A Dynamic oxygen transfer coefficient measurement method for column reactors

Abstract Dynamic oxygen transfer experiments in columns are modelled using an unsteady state, two-phase dispersion model for the column, and a second-order lag

Fermenter Scale-Up Using an Oxygen-Sensitive Culture

Abstract Scale-up investigations using an oxygen-sensitive Bacillus subtilis culture have been made in three nearly geometrically-similar aerobic fermenters of 45 L, 450 L and 4500 L size gassed and gassed power were measured with strain gauges and electrical power. The correlation of Joshi et al. (1982) was used to derive relations for the dependency of gassed power uptake on scale factor and stirring speed for constant superficial gas velocity. The product selectivity ratio (acetoin/butanediol) was measured from batch cultures and correlated only roughly with power uptake per unit volume. The ratio of time constants for circulation and reaction of dissolved oxygen indicated possible roles of surface aeration and local oxygen depletion.

A POROUS MEMBRANE-CARRIER GAS MEASUREMENT SYSTEM FOR DISSOLVED GASES AND VOLATILES IN FERMENTATION SYSTEMS

ABSTRACT Porous Teflon has a very high permeability for gases and volatile compounds in aqueous solution. Applying the carrier gas tubing method, it can be combined with (a) suitable gas detector(s) to measure different compounds using a probe of very small dimensions (i.e. 380 mm2 membrane surface). This method was successfully tested with different gases (CO2, CH4) and volatiles (methanol, ethanol, acetone, butanol). For O2 a much larger membrane area was necessary (100 cm2) to obtain a sufficiently high partial pressure in the gas outlet stream. The small probe responded rapidly with time delays from about 5 to 60 s. The steady-state calibration curves were linear. A very promising arrangement for analysis in fermentation would be the combination of this method with a mass spectrometer, which would allow gas and liquid phase analysis with a conventional continuous capillary gas inlet system.

Bubble column fermenter modeling: A comparison, for pressure effects

Abstract Two models which describe the oxygen transfer, oxygen uptake, and axial mixing in a bubble column fermenter are described. Model I includes no pressure effects and can be solved analytically. Model II incorporates the influence of hydrostatic pressure on oxygen solubility and gas expansion and must be solved numerically. The liquid phase oxygen concentration profiles as obtained from both models are compared to ascertain for what parametric conditions and for what maximum column height Model I is valid. The results show that for many situations Model I can approximate the oxygen profiles in a 10 m column within 20%. As the transfer and uptake rates increase the deviation of Model I can reach 80% for a 10 m column.

A Microbial Culture as an Oxygen Sensor for Reactor Mixing Effects

The influence of mixing on the scale-up of fermentation processes is characterized by considerable uncertainty. Classical methods for scale-up call for keeping the geometry similar while maintaining one key parameter constant. Unfortunately the result is that other key parameters will change greatly with scale.’ Some thought has been given to scaling-down and devising a poorly mixed laboratory reactor to mimic the large-scale mixing effects.* Since basic studies are lacking, these mixing effects are largely unknown, and thus it is impossible to establish a correct mixing model for a smaller scale. Mixing studies would be facilitated by the availability of a suitable mixingsensitive microbial culture. Such a culture should possess the following characteristics: ( I ) (2) rapid response (3) ease of monitoring (4) fast growth (5) growth under nonsterile conditions (6) good reproducibility The present report gives results with a microbial culture that has these charactehstics and appears to have great promise as a tool for the study of mixing effects in fermenters. sensitivity to varying substrate levels