bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of fermentation behavior and formulation of a semidefined nutrient medium based on acid‐production measurements in Z. mobilis cultures
Authors: Veeramallu Uday , Agrawal Pramod
Published: December 2004

Batch fermentations of glucose to ethanol by Z. Mobilis.(ATCC 10988) were examined in several semidefined nutrient media. The measurement of acid produced by the microorganism was used to study its transient fermentation characteristics. Limitation of nitrogen source in the semidefined medium of Rogers and coworkers2 was found to limit the growth of this microorganism in the late stages of batch fermentations, when the initial glucose concentration was 75 g/L and higher. The microorganism exhibits a preference for inorganic nitrogen over preformed organic nitrogen provided by yeast extract. The microbial growth occurs exponentially in the presence of ammonium sulfate and yeast extract. However, in the absence of ammonium sulfate, the growth occurs in a linear fashion. The “linear” growth phase is characterized by poor cell‐mass yields, and during this phase, growth and ethanol production are decoupled. An improved semi‐defined growth medium is established which supports better growth rate and cellular yield, without affecting the ethanol yield.
Characteristic reaction paths of biochemical reaction systems with time scale separation
Authors: Liao James C. , Lightfoot Edwin N.
Published: December 2004

A technique has been developed for characterizing the in vivo behavior of key enzymes from intermediate measurements. The technique is based on the identification of characteristic reaction paths, and it depends on the time scale separation characteristics of the systems. It is shown that useful information can be obtained from the phase plots of properly selected intermediate pairs or combinations which typically show process insensitive algebraic relations approached on time scales short compared to those of most practical interest. These characteristic reaction paths provide useful global measures of enzyme activity. The mathematical basis of reaction path analysis is investigated using linear transformation techniques. General theorems are developed predicting the existence of characteristic reaction paths as asymptotic limits whenever there is effective time scale separation. These limits are reached when fast reactions are relaxed, and available evidence suggests that these conditions will occur for the majority of reaction networks.
Application of characteristic reaction paths: Rate‐limiting capability of phosphofructokinase in yeast fermentation
Authors: Liao J. C. , Lightfoot E. N. , Jolly S. O. , Jacobson G. K.
Published: December 2004

The intracellular rate‐limiting capability of phosphofructokinase in baker's yeast (Saccharomyces cerevisiae) fermentation is investigated using the reaction path analysis discussed by Liao and Lightfoot in a previous article. It is found that the yeast cells under our experimental conditions indeed exhibit the characteristic behavior, and the characteristic reaction path on the G6P‐ATP phase plot is determined for cells fed with different sugars, cells of different strains, and cells in the transition period following rehydration. Results suggest that phosphofructokinase does not limit the CO2 production rate of the cells under investigation. However, it is not present in a great excess either: ca. 80% of phosphofructokinase activity is utilized by the glycolytic pathway of the cell under investigation.
Simultaneous measurements of oxygen diffusion coefficients and solubilities in fermentation media with polarographic oxygen electrodes
Authors: Ju Lu‐Kwang , Ho Chester S. , Baddour Raymond F.
Published: December 2004

A membrane‐covered oxygen electrode was used to measure oxygen diffusion coefficients and solubilities in aqueous glucose solutions and various fermentation media following a newly developed methodology. The fermentation media studied were tryptic soy broth and those for fermentations of Penicillium chrysogenum, Saccharomyces cerevisiae, and Micrococcus glutamicus. The experimental results of oxygen diffusion coefficients and solubilities in glucose solutions were in good accord with the literature data. As for the fermentation media, both oxygen diffusion coefficients and solubilities were found to decrease with an increased fractional composition of these media, and log‐additive behaviors of the oxygen diffusion coefficients and solubilities in fermentation media were observed.
Controlling fermentation of lignocellulose hydrolysates in a continuous hollow‐fiber reactor using biosensors
Authors: Mandenius Carl Fredrik
Published: December 2004

Fermentation of lignocellulose hydrolysates as spent sulfite liquor or as hydrolysate from sulfur‐dioxide‐treated wood to ethanol has been controlled by using biosensors for glucose and ethanol. Yield and productivity were studied with respect to concentration level of the metabolites in a continuous hollow‐fiber reactor. High constant yield was achieved by controlling the glucose to low concentration levels. Reduced productivity were obtained when fermenting at high ethanol concentrations as an effect of inhibition of the yeast cells. The observations emphasize the advantage of controlling the process to favorable concentrations of monosaccharides and ethanol.
Optimization of microalgal production in a shallow outdoor flume
Authors: Laws Edward A. , Taguchi Satoru , Hirata Janice , Pang Lance
Published: December 2004

The marine diatom Cyclotella cryptica was grown over a period of 13 months in a 48‐m2 shallow outdoor flume. The use of foil arrays at intervals of 1.2 m to effect systematic vertical mixing in the flume was found to significantly enhance microalgal production (p = 0.006). Average photosynthetic efficiencies (based on visible irradiance) with and without the foil arrays in place were 9.6 ± 0.8 and 7.5 ± 0.5% (±95% confidence intervals), respectively. A cost–benefit analysis indicated that the foil arrays were cost‐effective if the value of the algae exceeded about $2.28 kg1 of ash‐free dry weight (AFDW). Parallel experiments performed in four 9.2‐m2 flumes showed that production was maximized when the cells were grown on a 2‐day batch cycle between harvests rather than on a 1‐ or 3‐day batch cycle. The optimum initial concentration (immediately after harvesting) of the algae was negatively correlated with the time interval between harvests and ranged from approximately 39 g AFDW/m3 on a 3‐day cycle to 213 g AFDW/m3 on a 1‐day cycle. The increase in production resulting from growth on a 2‐day rather than a 1‐day batch cycle was about 19% and was statistically significant at p = 0.0003. Growth of C. cryptica over a total period of 122 days during the 13‐month study in the 48‐m2 flume under near‐optimal conditions (2‐day batch cycle, initial concentration 155 g AFDW/m3) resulted in an average production rate (±95% confidence interval) of 29.7 ± 2.7 g AFDW/m2 d.
Limited modifications of soya proteins by immobilized subtilisin: Comparison of products from different reactor types
Authors: Herbert A. B. , Dunnill P.
Published: December 2004

A comparison of different immobilized enzyme reactors has been made for the limited modification of soya storage proteins and the products compared with those from action of the soluble enzyme. Clarified total water extracts of soya protein were subjected to the action of subtilisin in a soluble and immobilized form. The sodium dodecyl sulfate (SDS) electrophoresis patterns of soya proteins modified by enzyme in the two forms differed for unbuffered soya protein at the same pH of 8.0. However, identical patterns could be obtained by a downward adjustment of the pH of soya protein treated with immobilized enzyme. The same SDS electrophoresis pattern could be obtained for a packed column of immobilized enzyme and a well‐mixed vessel by buffering. Operation of the column reactor at higher superficial linear velocities (above 1.47 cm/min), higher protein concentrations (8.8% w/v), and prolonged periods (24 h) led to a bed compression attributed to the protein coating of the support.
A batch reactor mass transfer kinetic model for immobilized biomass biosorption
Authors: Tsezos M. , Noh S. H. , Baird M. H. I.
Published: December 2004

Inactive cells of Rhizopus arrhizus have been immobilized into the form of particles of desirable particle size using a proprietary immobilization technique. The immobilized biomass particles are porous and are members of a new generation of biological origin adsorbents. The uranium adsorptive behavior of the biosorbent particles was modeled using a batch reactor mass transfer kinetic model of the biosorption process. The model successfully predicts the batch reactor adsorbate (uranium) concentration profiles and has provided significant insights on the way biosorbents function.
Operation of a three‐phase biofilm fluidized sand bed reactor for aerobic wastewater treatment
Authors: Ryhiner G. , Petrozzi S. , Dunn I. J.
Published: December 2004

A biofilm fluidized sand bed column reactor (14 L) has been operated in the three‐phase mode on a soluble glucose‐yeast hydrolysate substrate in which the biofilm‐sand phase (1‐2.5 L) was suspended by direct aeration of the bed. Within two weeks a tight biofilm was formed whose activity resulted in a 90% reduction, with loads of 10.7 kg TC/m3day. The residence time was 1 h. The biofilm remained intact during operation with high residence times (up to 23 h) over three weeks. Oxygen transfer coefficients varied with aeration rate and sand quantity between 0.02 and 0.04 s−1 during non growth conditions; they decreased with increasing amounts of clean sand and were higher and relatively independent of the sand fraction with biofilm‐covered sand. Aeration rates used in the 14 L reactor were 23‐40 L/min (2.4‐4.1 cm/s) and were sufficient to suspend 78‐92% f the biofilm‐covered sand. Clean sand was 50‐75% suspended. Oxygen uptake rates varied between 15.4 and 23.1 mol/m3 h.
The use of image analysis for morphological measurements on filamentous microorganisms
Authors: Adams H. L. , Thomas C. R.
Published: December 2004

Characterization of mycelial morphology is important for the design and operation of filamentous fermentations. Initial investigations have been made of semiautomated image analysis as a replacement for a digitizing‐table method. It was shown that the image analysis method was more precise than the digitizing‐table method used, although this extra precision is unimportant in this application. On average, image analysis gave mean hyphal lengths 6% greater than digitizing, because the latter used chord lengths to represent are lengths. For short branches image analysis was less accurate. In time and convenience the image analysis method had an overwhelming advantage, and this advantage might be enhanced by full automation. The resulting ability to characterize mycelial morphology rapidly would permit such characterization to be used routinely in studies of filamentous fermentations.
A stirred bath technique for diffusivity measurements in cell matrices
Authors: Chresand Thomas J. , Dale Bruce E. , Hanson Shari L. , Gillies Robert J.
Published: December 2004

A stirred bath technique was developed for determining effective diffusivities in cell matrices. The technique involves cell immobilization in a dilute gel which has negligible effect on solute diffusion. Agar and collagen were tested as immobilizing gels. Agar gel was shown to have minor interactions with the diffusion of various biological molecules, and was used for immobilization of Ehrlich Ascites Tumor (EAT) cells. Diffusivities of glucose and lactic acid were measured in EAT matrices for cell loadings between 20 and 45 vol %. Treatment with glutaraldehyde was effective in quenching the metabolic activity of the cells while preserving their physical properties and diffusive resistance. The measured data agree favorably with predictions based on Maxwell's equation for effective diffusion in a periodic composite material. The stirred bath technique is useful for diffusivity determinations in immobilized matrices or free slurries, and is applicable to both microbial and mammalian cell systems.
Centrifugal dewatering of acid casein curd: Effect of casein manufacturing and centrifugation variables on curd compression in a laboratory centrifuge
Authors: Munro P. A. , Van Til H. J.
Published: December 2004

Data relevant to curd compression in a horizontal, solid bowl decanter centrifuge have been obtained by studying the dewatering of acid casein curd in a batch laboratory centrifuge. Analysis of curd compression under centrifugal force predicts a moisture content gradient in the dewatered curd from a maximum at the curd–liquid interface to a minimum at the centrifuge bowl wall. This moisture content gradient was also measured experimentally, and its practical implications are discussed. Increases in centrifugal force, centrifugation time, and centrifugation temperature all caused a marked de crease in dewatered curd moisture content, whereas in creases in precipitation pH and maximum washing temperature caused a smaller decrease in dewatered curd moisture content.
Bacterial deposition on and detachment from surfaces in turbulent flow
Authors: Hermanowicz S. W. , Danielson R. E. , Cooper R. C.
Published: December 2004

A number of experimental studies on deposition and detachment of bacterial cells of Pseudomonas sp. was performed in an inclined plate apparatus 2.3 m long. In each run, ca. 108cells were introduced into a layer of flowing water at Reynolds numbers of ca. 1000 and 1300. After a preset time, the flow was stopped and the position of attached cells measured. Spatial pattern of attached cells was initially aggregative and remained so for lower flow rates. For higher flow rates the pattern tended towards randomness, perhaps as a result of cell detachment. Overall sticking efficiency of cells was very small (ca. 10−5).
Dynamics of foreign protein secretion from Saccharomyces cerevisiae
Authors: Park Seujeung , Ramirez W. Fred
Published: December 2004

A mathematical model describing the dynamics of foreign protein secretion from yeast cells is developed. The secretion events, which are a series of complicated enzymatic reactions and carrier‐involved transport, are lumped to a practically applicable model structure, based on the major interactions between the heterologous polypeptides and the host cell's secretory machinery through the pathway. The developed model structure predicts that the secretion rate constant is represented as a saturated form with respect to the host cell's specific growth rate. The validity of the proposed model structure is tested by generating dynamic response data to a step input of cycloheximide. The model system used in the experiment is SEY2102‐s21, which has an integrated copy of a yeast secretion‐mutant invertase that simulates well typical gene cassettes designed to secrete mature foreign proteins utilizing the yeast cell's secretion signals. Protein quantification is done by gel electrophoresis followed by immuno‐blot on nitrocellulose filters and subsequent scanning with a reflectance densitometer. Experimental data confirm the proposed model structure.
Modeling of contact‐inhibited animal cell growth on flat surfaces and spheres
Authors: Cherry Robert S. , Papoutsakis Eleftherios Terry
Published: December 2004

A model of contact‐inhibited growth of cells on flat and spherical surfaces is presented. It shows that contact inhibition does not significantly affect the calculated growth rate of cells unless they are allowed to multiply a large amount from the original seeding density. Microcarriers seeded at low densities require long times to reach confluence because contact inhibition becomes important. In systems with both growth and separate cell death, the equilibrium fraction of holes in the confluent monolayer is below 8% if the death rate is less than half the growth rate, but increases rapidly as the death rate increases from that value.
The effect of enzyme concentration on the rate of the hydrolysis of cellulose
Authors: Sattler W. , Esterbauer H. , Glatter O. , Steiner W.
Published: December 2004

The relationship among extent of hydrolysis, reaction time, and enzyme dosage was investigated. For this, Sigmacell 50 and pretreated poplar wood (20 g/L) was hydrolyzed with varying dosages of cellulases from three different sources (5 to 100 FPU/g) for time periods ranging from 2 to 94 h. It was found that the formation of glucose can be described by summation of two parallel first order reactions. The extent of hydrolysis at fixed time increases with increasing enzyme dosage in a hyperbolic function. From the empirical data it is possible to calculate the fractions of easily and difficult hydrolyzable cellulose and the digestability which could maximally be obtained at infinite enzyme loadings. In the system Sigmacell 50 and Celluclast the easily and difficult hydrolyzable components are 43.0 and 57.0%, respectively, and the maximum digestability at 94 h is 82.6%. Poplar wood, steam treated at 200°, 220°, and 240°C, showed with Celluclast at 24 h a maximum digestability (weight percentage of wood degraded to glucose) of 43.9, 64.9, and 68.0%. The relationships derived from experimental data allow one to compare objectively the effectiveness of different cellulase enzymes and different pretreatments.
Design of a lamella settler for biomass recycling in continuous ethanol fermentation process
Authors: Tabera J. , Iznaola M. A.
Published: December 2004

The design and application of a settler to a continuous fermentation process with yeast recycle were studied. The compact lamella‐type settler was chosen to avoid large volumes associated with conventional settling tanks. A rationale of the design method is covered. The sedimentation area was determined by classical batch settling rate tests and sedimentation capacity calculation. Limitations on the residence time of the microorganisms in the settler, rather than sludge thickening considerations, was the approach employed for volume calculation. Fermentation rate tests with yeast after different sedimentation periods were carried out to define a suitable residence time. Continuous cell recycle fermentation runs, performed with the old and new sedimentation devices, show that lamella settler improves biomass recycling efficiency, being the process able to operate at higher sugar concentrations and faster dilution rates.
Dynamic modeling of immobilized cell reactor: Application to ethanol fermentation
Authors: Nakasaki Kiyohiko , Murai Takeji , Akiyama Tetsuo
Published: December 2004

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.
Characterization of production of free gluconic acid by Gluconobacter suboxydans adsorbed on ceramic honeycomb monolith
Authors: Shiraishi Fumihide , Kawakami Koei , Kono Seiji , Tamura Akihiko , Tsuruta Satoshi , Kusunoki Koichiro
Published: December 2004

Gluconobacter suboxydans IFO 3290 was immobilized by adsorption on ceramic honeycomb monolith and continuous production of free gluconic acid from glucose was performed in an aerated reactor. The effects of reactor residence time, aeration rate, and glucose concentration were investigated on the gluconic acid yield. Observation of SEM photographs revealed that the cells were adsorbed with a high density not only on the outer surface of the support but also on the inner surface of large pores. From measurement of the number of the adsorbed cells, it was elucidated that the biofilm comprised a monolayer or bilayer of the cells. Maximum specific rate of growth was estimated for the free and adsorbed cells, and the adsorbed cells were found to grow at a fast rate compared with the free cells. In the continuous fermentation performed for one month at the glucose concentration of 100 kg/m3, reactor residence time of 3.5 h and aeration rate of 900 cm3/min, the activity of the adsorbed cells was appreciably stable. The high productivity of 26.3 kg/(m3‐reactor · h) was attained with the gluconic acid yield of 84.6% and glucose conversion of 94%.
Further kinetic characterization of alginate‐entrapped cells of Mucuna pruriens L.
Authors: Pras Niesko , Hesselink Paul G. M. , Guikema Wiebout M. , Malingré Theo M.
Published: December 2004

Alginate‐entrapped cells of Mucuna pruriens L. hydroxylate L‐tyrosine, tyramine, para‐hydroxyphenylpropionic acid, and para‐hydroxyphenylacetic acid to their corresponding catechols, which were released into the incubation medium. Michaëlis‐Menten kinetics was applied for each bioconversion. The apparent affinity constants were comparable with the affinity constants obtained with a homogenate directly prepared from the cells used for entrapment and with a derived partly purified phenoloxidase. The values found for the apparent maximum rates of bioconversion of the entrapped cells were ca. 50% of the values of the maximum rates of bioconversion of the cell homogenate, indicating that the entrapped cell system was not operating optimally. The effective diffusivities of the substrates and products were measured with alginate‐entrapped, inactivated cells. From the five inactivation methods tested, glutaric aldehyde treatment was chosen as the general procedure. Calculated effective diffusivities for the monophenols and catechols demonstrated that these compounds could diffuse freely into and out of the beads. For each bioconversion, the observable modulus was calculated from the initial rate of bioconversion and the effective diffusivity of the substrate. The resulting values indicated that the diffusional supply rate of the substrates was not the limiting factor, except for the conversion of tyramine for which a modulus higher than one was obtained. Analogously, the observable moduli were calculated for oxygen, which was utilized for bioconversion and cell respiration, and these values pointed towards strong oxygen limitation in all cases. The bioconversion rates of the entrapped cells increased with decreasing cell aggregate size. Therefore, it was concluded that direct cell‐matrix contact determined the amount of phenoloxidase involved in the bioconversions. The bioconversion rate on a protein basis was constant with enhancement of the bead charge and thus, in spite of limitations, the mixing conditions as such were relatively optimal. In conclusion, the nonoptimal efficiency of the plant cell system studied was caused by oxygen limitation and a partial phenoloxidase participation, but not by mass transfer limitations for substrates and products with the exception of the conversion of tyramine into dopamine.
Characteristics of immobilized lipase‐catalyzed hydrolysis of olive oil of high concentration in reverse phase system
Authors: Kang Sung Tae , Rhee Joon Snick
Published: December 2004

Candida rugosa lipase immobilized by adsorption on swollen Sephadex LH‐20 could almost completely hydrolyze 60% (v/v) olive oil in isooctane. Kinetic analysis of the lipase‐catalyzed hydrolysis reaction was found to be possible in this system. Amount of fatty acids produced was linearly proportional to the enzyme concentration of 720 μg/g wet gel. The specific enzyme activity was 217 units/mg protein at 60% (v/v) olive oil concentration. When the initial rate is plotted versus concentration of olive oil, this system did not follow Michaelis‐Menten kinetics. Maximum activity was obtained at pH 7, but optimum temperature shifted towards higher one with the increase of olive oil concentration. Among the various chemical compounds tested, Hg2+ and Fe2+ inhibited the lipase seriously. As the concentration of olive oil increased, the rate of the hydrolysis also increased, but degree of the hydrolysis was observed to decrease. The supply of water from the inside of the gel to the surface of the gel was the main factor for the control of the rate of hydrolysis in batch hydrolysis. The immobilized lipase was used to hydrolyze olive oil two times. Achievement of chemical equilibrium took a longer time with the addition of water and the degree of hydrolysis decreased in the second consecutive trial. After the second hydrolysis trial, the gels were regenerated in a packed column first by eluting out both residual fatty acids around the gel particles and the accumulated glycerol with ethanol and then with 0.05M phosphate buffer, pH 7. The immobilized lipase on the regenerated gel showed the same hydrolysis activity as the original one.
Effect of number of turbine impellers on surface aeration in laboratory fermentor
Authors: Veljković Vlada , Skala Dejan
Published: December 2004

The effect of one and two four‐flat‐bladed turbine impellers on the surface aeration intensity in a laboratory tormentor was investigated at different agitation speeds and sparge rates. The surface aeration was found to be generally more intensive with two impellers for the same other operating conditions because of higher power consumption and the position of the upper impeller closer to the free liquid surface. The surface aeration intensity was successfully correlated in terms of power consumption and sparge rate. The aeration number alone cannot be used for general predicting surface aeration intensities.
Biotransformation of acrylonitrile to acrylamide using immobilized whole cells of Brevibacterium CH1 in a recycle fed‐batch reactor
Authors: Hwang Jun Sik , Chang Ho Nam
Published: December 2004

Acrylamide was produced from acrylonitrile using immobilized Brevibacterium CH1 cells that were isolated from soil and found to possess nitrile hydratase activity. The reaction conditions and stability of the enzyme activity were studied. The conversion yield was nearly 100%, including a trace amount of acrylic acid. This strain showed strong activity of nitrile hydratase toward acrylonitrile and extremely low activity of amidase toward acrylamide. A packed bed reactor was operated in a fed‐batch manner for acrylamide production of high concentration. The acrylonitrile concentration was maintained below 3% and the operating temperature at 4°C to minimize enzyme deactivation.
Medium‐induced inhibition of microbial adsorption to nickel and activated charcoal
Authors: Protheroe R. G. , Cumming R. H. , Matchett A.
Published: December 2004

Equilibrium adsorption studies on Escherichia coli and Saccharomyces sp. revealed the capacity and affinity of these organisms for the surfaces of powdered charcoal and nickel. In simple salt solutions both organisms readily adsorbed to each solid with an affinity and maximum loading capacity individual to each cell–solid combination. In the presence of common growth media (lab‐lemco, nutrient broth, peptone, and yeast extract, individually at a concentration of 1.3%), each medium substantially inhibited adsorption. Each medium contained a protein‐aceous constituent as determined by ultraviolet (UV) analysis. The degree of inhibition was relative to medium concentration present during assay. Cell wall extracts from whole‐yeast cells also effectively inhibited adsorption. Cells adsorbed in the presence of sodium chloride solutions were susceptible to subsequent desorption by nutrient broth.
Dependence of in vivo inactivation kinetics of gramicidin S synthetase on cell physiology
Authors: Tasker James C. , Agathos Spiros N.
Published: December 2004

Gramicidin S synthetase, the enzyme complex catalyzing the biosynthesis of the antibiotic gramicidin S in Bacillus brevis, is subject to O2‐dependent in vivo inactivation during exponential aerobic growth after reaching a peak in specific activity. The five amino acid substrates of the synthetase are capable of stabilizing its activity to varying degrees in whole cells shaken aerobically. Depending on the time of cell harvesting before, during, or after the peak in intracellular gramicidin S synthetase specific activity, the enzyme has a long, medium, or short half‐life, respectively. The kinetic profiles of gramicidin S synthetase in B. brevis cells indicate that both the kinetics of synthetase loss and the degree of its amino‐acid‐mediated stabilization are a strong function of the cells' physiological development.
Improvement of aerobic treatment process by cross‐linked polyvinylpyridine
Authors: Kawabata Nariyoshi , Oda Masakatsu
Published: December 2004

In continuous aerobic treatment of artificial sewage by activated sludge, the rate of removal of chemical oxygen demand (COD) was markedly enhanced by the presence of cross‐linked poly‐4‐vinylpyridine (PVP). The concentration of dissolved oxygen (DO) was also low in the presence of PVP. The extent of improvement in COD removal increased with increases in substrate load and the surface area of the PVP in the working space of the test apparatus. These results suggest an increase of the bacterial population resulting from the presence of the PVP. However, formation of measurable biofilm was not detected on the surface of the PVP during continuous aerobic treatment.
Optimization of fermentation processes using recombinant Escherichia coli with the cloned trp operon
Authors: Park Tai Hyun , Seo Jin‐Ho , Lim Henry C.
Published: December 2004

Optimal operating conditions have been determined for recombinant Escherichia coli cells in a fed‐batch and two‐stage continuous fermentors. The model expression system used in this article was the E. coli trp promoter cloned on plasmids. Model equations for cell growth and cloned‐gene expression have been formulated and used to evaluate process performances under different operating modes. The operating variables manipulated for maximum performance include the timing of IAA addition to derepress transcription from the trp promoter. The total operating period and the nutrient concentration profile during fermentations. For a fed‐batch mode, the performance was significantly improved by adjusting the IAA addition (environmental switch) time relative to the total operation period. It was found that the optimal switching time exists for a given total operation period. For a two‐stage continuous fermentation system, the productivity is more sensitive to the combination of the dilution rates than to the volume ratio of two reactors. In general, as long as the down time is less than the total operation time in the fed‐batch mode, the fed‐batch mode gives higher productivity than the two‐stage continuous system.
Assessment of macroenergetic parameters for an anaerobic upflow biomass bed and filter (UBF) reactor
Authors: Guiot S. R. , Podruzny M. F. , McLean D. D.
Published: December 2004

This article reports the steady‐state performance of two hybrid anaerobic digesters treating soluble synthetic sugar wastes of 1 and 0.5% strength and the assessment of the associated macroenergetic parameters (growth yield, so‐called maintenance coefficient). A theoretical development shows a “nongrowth” parameter concept to be more appropriate than maintenance or decay. Combined energy and mass balances are used to develop a model for growth rate which compares well with experimental data. The COD removal efficiency had no significant effect on growth yield and the maintenance parameter, although a dual combined balance indicated the possibility of such an effect. Macroenergetic parameters did not vary significantly with the specific feeding rate of the system. We thus conclude that a single model may be used over a broad range of feeding and performance conditions.
Extraction of monocrotaline from Crotalaria spectabilis using supercritical carbon dioxide and carbon dioxide–ethanol mixtures
Authors: Schaeffer Steven T. , Zalkow Leon H. , Teja Amyn S.
Published: December 2004

Monocrotaline, a pyrrolizidine alkaloid of chemotherapeutic interest, was successfully extracted from the crushed seeds of Crotalaria spectabilis using supercritical carbon dioxide and ethanol mixtures. Overall solubilities of the plant material in the supercritical fluid phase were as high as 1.1 mass percent, and monocrotaline solubilities were as high as 0.07 mass percent. The solubility of monocrotaline in the presence of other plant material was smaller by 50 to 98% compared with the solubility of pure monocrotaline in the supercritical fluid. Also, it was found that the extraction of the complex plant material was time‐dependent after approximately one percent of the original mass of the material had been extracted.