bluuebunny/crossref_metadata_2025 huggingface dataset:
Calculation of mean cell residence time for unsteady‐state activated sludge systems
Authors: Vaccari David A. , Fagedes Tom , Longtin Jon
Published: December 2004

A formulation to calculate the mean cell residence time (MCRT or sludge age) of unsteady‐state activated sludge systems is presented. The formulation was studied by applying it to data generated by computer simulation and to data obtained from an actual wastewater treatment plant. The computer simulation study allowed the effects of step and pulse changes in biochemical oxygen demand (BOD) loading, and step changes in a control variable, waste sludge flow rate, to be studied independently of each other and of other disturbances. The unsteady‐state MCRT formulation (herein called the dynamic sludge age, or DSA) was found to be an improvement over the traditional steady‐state calculation, both for process control, and for research into activated sludge dynamics.
Purification of glucagon by subunit exchange chromatography
Authors: Carrea Giacomo , Pasta Piero , Antonini Eraldo
Published: December 2004

Glucagon was immobilized onto Sepharose matrices activated with CNBr or tresyl chloride, as a function of several parameters including pH of coupling, concentration of added polypeptide, and presence or absence of urea. The hormone was linked to the matrix through a single point per molecule, namely, the ε ‐amino group of Lys12 when the coupling was carried out at alkaline pH, or the imidazole group of His1 when the coupling was carried out at acidic pH. Glucagon immobilized at alkaline pH interacted specifically with soluble glucogon. The extent of self‐association was similar to that of free glucagon, which exists in solution in a monomer–trimer equilibrium whose association constant is highly dependent on the characteristics of the buffer (pH, ionic strength, and nature of anions). The immobilized hormone proved to be suitable for the purification of the free one from a pancreatic extract. After a preliminary treatment with charcoal‐dextran, the extract was percolated on a glucagon–Sepharose column under associating conditions (high concentrations of salting out anions and alkaline pH) and then, following a washing to remove extraneous compounds, the specifically bound hormone was eluted under dissociating conditions (low ionic strength). The subunit exchange chromatography of the extract gave a ca. 90% pure product. The overall recovery of the process was ca. 66%. The leakage of immobilized hormone was 40% in the case of CNBr activation of Sepharose and 15% in the case of tresyl chloride activation, after an eight‐day treatment under working conditions.
On‐line estimation of mycelial cell mass concentrations with a computer‐interfaced filtration probe
Authors: Thomas Douglas C. , Chittur Venkatesh K. , Cagney Judy W. , Lim Henry C.
Published: December 2004

This article deals with the design and operation of a filtration probe for estimating cell concentrations in fermentations involving mycelial organisms such as Penicillium chrysogenum. This device, a much improved version of one developed previously, is placed directly into the fermentor and measures the filtration properties of the fermentation broth, which are correlated to the cell concentration. The probe is connected to a computer system which enables on‐line estimation of the cell concentration. Fiber‐optic light guides are used in combination with a pair of light sources and receivers to detect the relative position of the filter‐cake–fermentation‐broth interface. The lower sensor in the filtration tube enables reliable estimation of cell mass upto about 20 g/L (dry wt), while the upper sensor yields useful measurement of the filtration properties upto a concentration of about 40 g/L (dry wt) and appears to have the potential to go even higher. Major advantages of this probe system are the ease of measurement and the on‐line ability to measure very frequently, due to its nondestructive mode of operation. Thus, the probe obviates the need for manual sampling and reduces the risk of contaminating the culture. But, more significantly, it enables one to implement on‐line schemes including feedback control.
Optimization of the activity in porous media of proton‐generating immobilized enzymatic reactions by weak acid facilitation
Authors: Ruckenstein E. , Rajora P.
Published: December 2004

In addition to the role of maintaining the pH, buffers can also facilitate the transport of H+ ions in acid‐generating systems. The role of this facilitation in proton transport in porous pellets on acid‐generating immobilized enzymic reactions is examined. The activity in these systems can be maximized by a proper control of facilitation, which involves the determination of the appropriate variables out of (1) the concentration of the weak acid, (2) the pH of the medium, (3) the bulk substrate concentration, and (4) the type of weak acid. Since the intrinsic activity (IA) of the immobilized enzyme is such that it exhibits an optimum with respect to the pH, a partial (optimal) removal of diffusional limitation by facilitation maximizes the activity when the bulk pH is larger than this optimum pH. A complete removal of diffusional limitations, however, maximizes the activity when the bulk pH is less than or equal to the above optimum pH. The control of the diffusional resistance can be achieved by controlling the extent of facilitation, hence by adjusting the parameters mentioned above. Computations have been carried out to examine the effect of each of these parameters on the activity of the immobilized enzyme. It is found that when the bulk pH is less than or equal to the optimum pH of the intrinsic activity of the immobilized enzyme, there exists a lower limit on the amount of weak acid required to maximize the activity. However, an optimum amount of weak acid is required to maximize the activity when the bulk pH is higher than that optimum pH. For a given activity the amount of weak acid is minimal if the pK of the weak acid is close to the bulk pH. The effect of coupling between the proton and substrate transport on activity control is also examined and the effect of geometry on activity is evaluated for spherical, cylindrical, and flat‐plate configurations.
A new technique for the production of immobilized biocatalyst in large quantities
Authors: Hulst A. C. , Tramper J. , van't Riet K. , Westerbeek J. M. M.
Published: December 2004

A new technique is presented for the production of immobilized biocatalysts in large quantities. It consists of breaking up a jet of the biocatalyst/presupport mixture in uniform droplets by means of a resonance technique. Entrapment of yeast and plant cells in calcium alginate has been used as the model. The production capacity of the nozzles used (0.5, 0.8, and 1.1 mm exit diameters) is two orders of magnitude larger than the production capacity of the conventional techniques (maximum capacity with a 1.1‐mm nozzle diameter is 24 L/h). Depending on frequency, nozzle diameter, and volumetric flow rate, the bead size varies between 1 and 2 mm, with standard deviations of 3‐5% for yeast immobilization and 10‐15% for plant cells. The deactivation of both yeast and plant cells is small and comparable to that found in the corresponding conventional procedures.
A new batch calorimeter for aerobic growth studies
Authors: Dermoun Z. , Boussand R. , Cotten D. , Belaich J. P.
Published: December 2004

A microcalorimeter for aerobic growth studies, derived from a Tian Calvet differential apparatus, was successfully constructed. The calorimetric vessel was a short cylinder, which permitted a good exchange between the surface area and the gas phase. The time constant of the calorimeter was 3.6 min and the sensitivity 234 V/W. The thermochemical aspect of the aerobic growth of Escherichia coli on succinate, acetate, and glucose was investigated. This analysis revealed that the contribution of biosynthetic reactions varied with the substrate used and strongly influenced the heat evolution. The experimental metabolic enthalpy change was in good agreement with the predicted value for succinate and glucose growth. To explain the discrepancy between the two values observed for acetate growth we suggest that acetate metabolism may generate a by‐product which was not further oxidized.
Enzymatic hydrolysis of cellulose in aqueous two‐phase systems. II. Semicontinuous conversion of a model substrate, solka floc BW 200
Authors: Tjerneld Folke , Persson Ingrid , Albertsson Per‐Åke , Hahn‐Hägerdal Bärbel
Published: December 2004

A model substrate, Solka Floc BW 200, was semicontinuously hydrolyzed in an aqueous two‐phase system based on crude dextran and polyethylene glycol over a period of more than 450 h. With an initial concentration of 75 g/L and intermittent addition of cellulose an average concentration of 50 g/L sugar was semicontinuously produced at dilution rates of 0.006–0.012 h−1. The conversion of substrate varied between 49 and 66%. The enzyme consumption measured as FPU/g reducing sugar (RS) produced could be reduced by a factor two when compared to a batch process since, in the aqueous two phase system investigated, the enzyme could be recycled two times.
Effects of aromatic compounds on hemicellulose‐degrading enzymes in Aspergillus japonicus
Authors: Sharma A. , Milstein O. , Vered Y. , Gressel J. , Flowers H. M.
Published: December 2004

Aspergillus japonicus was grown in the presence of various aromatic compounds at 0.1 and 1 mg/mL, and extracellular xylanase and arabanase activities were measured. Some of the aromatic compounds tested, especially at the higher concentration, suppressed the appearance of hemicellulase activities, expressed as xylanase or arabanase. Vanillin at 1 mg/mL in the presence of either xylan or araban completely suppressed growth, and guaiacol and p‐coumaric acid markedly inhibited the growth of A. japonicus. The effects of the aromatic compounds on the activity of crude enzyme preparations were also ascertained. In vitro arabanase activity was affected more than xylanase activity.
Immobilized live cell reactor dynamics following dilution rate shift to growth conditions: Cell synchrony effects
Authors: Bailey Kevin M. , Venkatasubramanian K. , Karkare Subhash B.
Published: December 2004

Nutrient deprivation was used to synchronize an immobilized live cell culture of Acetobacter suboxydans. The substrate supply was increased by a step change in the dilution rate to the reactor. Oscillations in cell, substrate, and product concentrations were observed. A population balance model was developed to explain the observed reactor dynamics. Simulation results based on the model were used to substantiate the premise that cell synchrony is the likely phenomenon responsible for the observed oscillations. The implications of cell synchrony in immobilized cell systems are discussed briefly.
Semicontinuous affinity chromatography separations
Authors: McCoy B. J.
Published: December 2004

The semicontinuous operation of affinity chromatography columns charged and eluted alternately is studied mathematically. A strongly nonlinear adsorption equilibrium relation is utilized to examine the periodic mode of adsorption and desorption. The governing differential equations are solved by the method of characteristics. The time interval between desorption and adsorption periods is estimated, and implications for separations are discussed to show the advantages of semicontinuous cyclic operation.
Influence of H2 stripping on methane production in conventional digesters
Authors: Poels J. , van Assche P. , Verstraete W.
Published: December 2004

Hydrogen is a central metabolite in the methanization process. In this study the partial pressure of hydrogen in the gas phase of laboratory manure digesters was monitored over extensive periods of time and found to vary between 50 and 100.10−6 atm. By sparging the gas phase of the digester through an auxiliary reactor, hydrogenotrophic methanogens were allowed to develop at the expense of hydrogen and carbon dioxide present in the biogas, independently of the liquid or cell residence time in the main reactor. By scrubbing ca. 100 volumes of biogas per liter reactor per day through an auxiliary reactor, hydrogen concentration could be decreased maximally 25%. This resulted in an increase in the gas production rate of the main digester of ca. 10% and a concomitant improved removal of volatile fatty acids from the mixed liquor. The results obtained indicate that considerable stripping of hydrogen from the digester could be achieved at acceptable energy expenditure. However, the microbial removal of the hydrogen at these low concentrations is extremely slow and limits the applicability of this approach.
Immobilization of BSA, enzymes and cells of Bacillus stearothermophilus onto cellulose, polygalacturonic acid and starch based graft copolymers containing maleic anhydride
Authors: Beddows C. G. , Gil M. H. , Guthrie J. T.
Published: December 2004

Poly(maleic anhydride styrene) graft copolymers of cellulose, pectin polygalacturonic acid salt, calcium polygalacturonate, and starch were prepared and used to immobilize proteins. The cellulose grafts coupled quite appreciable quantities of acid phosphatase, glucose oxidase, and trypsin. However, the general retention of activity was somewhat disappointing. Further investigation with acid phosphatase showed that the amount of enzyme immobilized increased as the amount of anhydride in the graft copolymer increased but no such relationship existed for the enzymic activity. The cellulose graft copolymers were hydrolyzed and it appeared that the carboxyl group aided adsorption of the enzyme. Attempts to couple acid phosphatase using CMC through the free carboxyl groups, created by hydrolysis, gave only a small increase in the extent of protein coupling. However, the unhydrolyzed system gave a useful degree of immobilization of cells of Bacillus stearothermophilus, as did a poly(maleic anhydride/styrene)‐cocellulose system. Attempts to improve the activity by using grafts based on other polysaccharide supports met with mixed success. Pectin products were soluble. Polygalacturonic acid products were partially soluble and extremely high levels of enzymic activity were obtained. This was probably due in part to the hydrophilic nature of the system, which also encouraged absorption of the enzyme. Attempts were made to reduce the solubility by using the calcium pectinate salt. Immobilization of acid phosphatase and trypsin resulted in inceased protein coupling but relatively poor activities were attained. A starch based system gave similar results. Calcium polygalacturonate was used to prepare an insoluble graft copolymeric system containing acrylonitrile‐comaleic anhydride. The resulting gels gave excellent coupling with acid phosphatase which had a very good retention of activity.
Parameters affecting optimum activity and stability of urokinase‐bound fibrocollagenous tubes
Authors: Senatore Fred , Bernath Fred
Published: December 2004

Urokinase was immobilized by entrapment to fibrocollagenous tubes in order to develop a small‐caliber fibrinolytic vascular prosthesis. Several parameters associated with the immobilization process were studied in order to optimize bound urokinase activity and stability. A total of 37% of the absorbing enzyme was attached to the collagen tube and 38% of the attached enzyme retained esterolytic activity, under optimal conditions. In the crosslink step of the entrapment process, the glutaraldehyde concentration was varied from 0.01 to 5.00% (i.e., 0.01, 0.1, 1.0, 3.0, and 5.0%). Urokinase activity was optimized at a 1.0% glutaraldehyde crosslink concentration. Urokinase‐bound fibrocollagenous tubes (UK‐FCT) prepared at the above glutaraldehyde concentrations were tested for their activity with time. The UK‐FCT's with 0.1, 1.0, and 3.0% glutaraldehyde retained constant activity for at least 75 h operation time. The UK‐FCT's with 0.1, 1.0, and 3.0% glutaraldehyde retained constant activity for at least 75 h operation time. The UK‐FCT's with 5.0 and 0.01% glutaraldehyde remained stable for the first 50 h operation time, but begandeactivating beyond 50 h. UK‐FCT'S Crosslinked with 0.01, 0.1, 1.0, and 5.0% glutaraldehyde were recrosslinked with 0.02% glutaraldehyde for 24 h, after they have been operating for 50 h, and the effect of reexposing the crosslink agent on the stability of the UK‐FCT's was studied. The results showed that 0.02% glutaraldehyde reexposure had no effect on 0.1, 1.0, and 5.0% glutaraldehyde crosslinked UK‐FCT's but exerted an inhibitory effect on a 0.01% crosslink density UK‐FCT. Several fibrocollagenous tubes were exposed to various glutaraldehyde concentrations prior to immobilizing urokinase. The subsequent immobilization process occurred under optimal conditions. The effect of the precrosslink step on the activity of the UK‐FCT was studied. Results indicated that UK‐FCT activity decreases as the precrosslink density increases. The UK‐FCT's made under optimal conditions remained stable for at least 75 h operation time, corresponding to ca.1 year of storage time. Ex vivo exposure of UK‐FCT's to whole canine blood did not affect catalytic activity. Implantation of a UK‐FCT by carotid arterial interposition via an end‐to‐end anastomosis and subsequent excision after 60 days resulted in an enhanced esterolytic activity which decreased with time to a level close to preoperative levels.
Patterns of aeration in a solid substrate fermentor through the study of the residence time distribution (RTD) of a volatile tracer
Authors: Gervais Patrick , Bazelin Christophe , Voilley Andrée
Published: December 2004

The injection of a volatile tracer in the gas flow allowed to describe the residence time distribution (RTD) in a solid substrate reactor. The chromatographic analysis of Dirac impulses of acetone led to identify the fermentor as a first‐order rate system. The evolution of the time constant (λ) of the system versus the gas flow rate gave a flow rate value that permitted a homogeneous aeration of the fermentor.
Fabrication of reusable enzyme brushes for clinical analyses: Lactate dehydrogenase enzyme brush
Authors: Raghavan K. G. , Ramakrishnan V.
Published: December 2004

A simple procedure for the entrapment of enzymes in nylon‐reinforced cellulose triacetate fibers and the fabrication of reusable enzyme brushes using such fiber bristles for the analytical determination of unknown samples have been described. As an example, enzyme brushes of lactate dehydrogenase were fabricated and were repeatedly employed for the determination of pyruvic acid in clinical samples in place of soluble enzymes. The above brush method compared well with that of wet enzymic analysis of pyruvate in clinical samples in accuracy, sensitivity, and reproducibility. The device also proved to be easy to handle, use, and reprocess for repeated analyses.
Deactivation of free and stabilized acid phosphatase by urea
Authors: Gianfreda Liliana , Marrucci Giuseppe , Greco Guido
Published: December 2004

Tests on acid phosphatase (E.G. 3.1.3.2) deactivation by urea have been performed at two pH values. Two conditions have been used: native enzyme operating batch‐wise in dilute solution and stabilized enzyme in continuous flow ultrafiltration membrane reactor. Stabilization is achieved by confining the enzyme within a concentrated solution of a linear chain polymer that forms a polarization layer over the membrane. The results provide significant information on the kinetics and thermodynamics of the complex phenomena taking place during deactivation. Deactivation by urea is also compared with thermal deactivation.
Depolymerization of chondroitin C Sulfate by immobilized Proteus vulgaris cells
Authors: Sato Nobuyuki , Murata Kousaku , Kimura Akira
Published: December 2004

Chondroitinase ABC catalyzing the depolymerization of chondroitin sulfate was induced by incubating the Proteus vulgaris cells in a medium containing chondroitin C sulfate as an inducer. Incubation of P. vulgaris cells for 12 h in the presence of 0.3% inducer was optimal to obtain the cells with highly active chondroitinase ABC. Such cells were immobilized in k‐carrageenan gel lattice, and some properties of chondroitinase ABC in immobilized cells were studied in comparison with those of the enzyme without immobilization (free enzyme). The stabilities of the enzyme toward heat and storage were remarkably improved by immobilizing the cells in k‐carrageenan gel lattice. Optimal pH and temperature for activity of the enzyme were slightly shifted to the alkaline region and higher temperature by immobilization and were 9.0 and 35°C, respectively.
A method for estimating the rejection coefficient–molecular weight relationship of ultrafiltration membrane for a chain polymer by using gel permeation chromatography
Authors: Adachi Shuji , Hashimoto Kenji , Komoto Mitsuaki , Tobita Hidetaka
Published: December 2004

An improved method is presented for estimating rejection coefficient‐molecular weight relationship of an ultrafiltration membrane for a polydisperse chain polymer. It is based on the basic idea using gel permeation chromatography originally developed by Cooper and Van Derveer. The method, in which peak spreading of an elution curve of the polymer was taken into consideration, is available for evaluating the relationship over a wide range of the molecular weight through only one experiment in analyses of the retentate and filtrate.
Growth dynamics of a methylotroph (Methylomonas L3) in continuous cultures. I. Fast transients induced by methanol pulses and methanol accumulation
Authors: Chu I‐Ming , Papoutsakis Eleftherios Terry
Published: December 2004

The dynamic behavior of the Ribulose Monophosphate‐type Methylomonas L3 in continuous cultures was studied, using methanol pulses to induce fast transients in steady‐state cultures of single (methanol) and mixed (methanol plus formaldehyde) substrates. In several experiments, the methanol‐uptake rate (MUR) profiles displayed negative MUR values for a time period following the methanol pulse, and significant amounts of methanol disappeared immediately following the pulse. These phenomena suggested the accumulation of methanol in the cells upon pulsing, apparently due to an active transport system. Accordingly, and in order to estimate the potential of the transport system for methanol accumulation, accumulation profiles were calculated for several pulse experiments. The calculations are based on a methanol balance and experimentally determined values of the cell volume and the true transient biomass yields. It is calculated that methanol accumulates up to 200‐fold to very high intracellular concentrations. The accumulation is calculated to be much higher in single‐ (methanol) substrate cultures of low dilution rate than in cultures of high dilution rate or of mixed substrates. The specific growth rate immediately following the methanol pulse decreased in single‐substrate cultures and increased in mixed‐substrate ones. The biomass yield decreased after the methanol addition in all experiments; however, the drop was less severe in the mixed‐substrate experiments. It is also suggested that formaldehyde as a methanol cosubstrate may be an effective means of providing more stable biomass yields and growth rates in reactors with imperfect mixing, and of protecting the reactor against accidentally induced methanol accumulation.
Properties and principles of mycelial flow: Experiments with a tube rheometer
Authors: Björkman Ulf
Published: December 2004

The flow behavior of a penicillin mash has been investigated with a tube rheometer and compared with rotational viscometer observations. In the low‐shear regions plug flow and breakdown of the plug have been studied. For turbulent flow turbulence damping was demonstrated. The Theological development during the fermentation was followed. At low deformation rates the pressure drop increased during the fermentation. In turbulent regions the opposite tendency was observed. The possible underlying flow mechanisms are discussed, and the influence of a number of physical parameters have been investigated.
Bioactive polymers XXX. Immobilization of invertase on the diazonium salt of 4‐aminobenzoylcellulose
Authors: Simionescu Cristofor , Popa Marcel I. , Dumitriu Severian
Published: December 2004

Invertase was immobilized on diazotized 4‐aminobenzoylcellulose. The optimum coupling conditions, namely enzyme concentration, time, and pH, were determined. The temperature and pH value for the maximum activity of the immobilized enzyme were determined and the apparent Michaelis constant was estimated.
Mathematical modeling of ethanol production by immobilized Zymomonas mobilis in a packed bed fermenter
Authors: Melick Michael R. , Karim M. N. , Linden J. C. , Dale B. E. , Mihaltz Pal
Published: December 2004

A mathematical model which describes ethanol production in a packed bed fermenter containing. Zymomonas mobilis entrapped in small spheres of calcium alginate within a packed bed fermenter has been developed. The equations combine simultaneous diffusion and reaction as well as a complex flow pattern to calculate glucose and ethanol profiles in the column type reactor. As part of the study, diffusivity values for glucose and ethanol in cell‐loaded calcium alginate were determined. Also a freecell kinetic expression for Z. mobilis at 33°C and ph 6.0 was developed. Comparison of the model with actual experimental results were made showing average deviations of ca. 30–40%.
Feasibility of enzymatic hydrolysis and alcoholic fermentation of starch contained in buffalo gourd (Cucurbita foetidissima) roots
Authors: Scheerens J. C. , kopplin M. J. , Abbas I. R. , Nelson J. M. , Gathman A. C. , Berry J. W.
Published: December 2004

The suitability of using annually grown, carrot‐sized buffalo gourd (Cucurbita foetidissima) roots as a feedstock for alcoholic fermentation was explored. Roots grown in 1982 and 1983 were slurried, dextrinized and saccharified using Takatherm™ and Diazyme™ (commercial enzymes manufactured by Miles Laboratories), and fermented by the action of Saccharomyces cerevisiae. These processes were monitored in detail and results were compared with those displayed by controls formulated using potato tubers. The preparation of gourd root slurries with suitable viscosity characteristics for enzymatic digestion required the addition of water (at least 50% by weight) which reduced the proportion of fermentable sugars in the resulting saccharified suspensions. The resulting slurries were well‐suited to enzymatic conversion of starch to sugar. Estimates of enzymatic efficiency in gourd root suspensions did not suggest the presence of naturally occurring amylase or glucosidase inhibitors in these plant materials. Saccharified gourd root mashes supported yeast growth well and produced ethanol yields at 82.2–86.5% of the theoretically maximum efficiency.
Fermentation kinetics of Zymomonas mobilis near zero growth rate
Authors: Jöbses I. M. L. , Hiemstra H. C. H. , Roels J. A.
Published: December 2004

The fermentation kinetics Zymomonas mobilis were studied near zero growth rate in fed‐batch cultures and continuous cultures with complete cell recycle. The results show the ethanol enhances that specific substrate conversion rate under these conditions. The maximum achievable ethanol concentration in continuous cultures with cell recycle (66 g/L) was significantly lower than in fed‐batch cultures (100 g/L). The results indicate that growth‐rate‐independent metabolism is not instantaneous and can lag behind steadily increasing ethanol concentrations in fed‐batch fermentations. A model is proposed to account for this slow adaptation.
Factors affecting the photoproduction of ammonia from dinitrogen and water by the cyanobacterium Anabaena sp. strain ATCC 33047
Authors: Ramos Juan L. , Guerrero Miguel G , Losada Manuel
Published: December 2004

Synthesis of ammonia from dinitrogen and water by suspensions of Anabaena sp. Strain ATCC 33047 treated with the glutamine synthetase inhibitor L‐methionine‐D,L‐sulfoximine is strictly dependent on light. Under otherwise optimal conditions, the yield of ammonia production is influenced by irradiance, as well as by the density, depth, and turbulence of the cell suspension. The interaction among these factors seems to determine the actual amount of light available to each single cell or filament in the suspension for the photoproduction process. Under convenient illumination, the limiting factor in the synthesis of ammonia seems to be the cellular nitrogenase activity level, but under limiting light conditions the limiting factor could, however, be the assimilatory power required for nitrogen fixation. Photosynthetic ammonia production from atmospheric nitrogen and water can operate with an efficiency of ca. 10% of its theoretical maximum, representing a remarkable process for the conversion of light energy into chemical energy.
The macrokinetic behavior of an enzymatic system with an enzyme inactivated in the reaction
Authors: Sud'ina G. F. , Kobel'kov G. M. , Varfolomeev S. D
Published: December 2004

This study deals with the behavior of a heterogeneous multisubstrate enzymatic system under enzyme inactivation in a reaction. Electronic computer modeling data have been obtained for its macrokinetics at different modes: (1) under mixed inflow of the substrates and (2) under their spatial separation. The enzymatic membrane exhibits low sensitivity to a change in the external conditions as the substrates are intermixed on the boundary. Quite the contrary, in the case of spatial separation of the substrates, the product flow from the membrane has displayed abrupt fluctuations at different boundary conditions. This work also looks into the arrangement of the reaction zones in the membrane and their transitions under different conditions.
Effect of cycling on final mixed culture fate
Authors: Stephens M. L. , Lyberatos G.
Published: December 2004

Cycling in feed substrate concentration and dilution rate is examined as a means of modifying the final fate of a mixed culture. It is shown for the case where the specific growth rate of one species is always greater than that of the second that no cycling strategy will provide the desired extinction of the faster growing species unless time delay is included in the modeling. To account for the time lag in adjusting organism metabolic activities to environmental changes, an adaptability parameter is introduced. Numerical simulations are carried out and an operating diagram indicating the conditions under which the desired extinction occurs is constructed. Cycling in feed substrate concentration and dilution rate are both found to produce the desired result.
The influence of immobilization and reduced water activity on gaseous‐alkene oxidation by Mycobacterium PY1 and Xanthobacter PY2 in a gas–solid bioreactor
Authors: Hamstra R. S. , Murris M. R. , Tramper J.
Published: December 2004

Immobilization of Mycobacterium PY1 and Xanthobacter PY2 in alginate and in or on hydroculture has a minor influence on the maximum rate of oxidation of propene and ethane. The apparent Km values of the immobilized cells are slightly higher than those of the free cells, indicating the presence of diffusion limitation in the immobilized systems. Both bacterial strains rapidly lose their alkene‐oxidizing activity when the water activity is decreased. This decrease in activity is so rapid that most of the activity is lost already when the pores of the pertinent supports are still filled with water. Therefore, it is not possible with this system to study the transition of mass transfer of substrates entirely in the water phase to mass transfer to substrates entirely through the gas phase.
Analysis of two interacting bacterial populations with opposite substrate preferences
Authors: Kim Sun Uk , Dhurjati Prasad
Published: December 2004

Interactions between two bacterial species which exhibit opposite substrate preferences in response to the same environmental conditions were investigated. Klebsiella oxytoca preferentially utilizes glucose over citrate as a substrate while Pseudomonas aeruginosa utilizes citrate over glucose. Both species were grown on single as well as mixed substrates, namely, D‐glucose and citrate, with various ratios of inocula and substrates. Competition is observed between the two species with citrate alone while amensalism is observed with glucose alone. In mixed cultures‐mixed substrates experiments, amensalism of K. oxytoca on P. aeruginosa prevailed until the exhaustion of glucose.
Some observations on the role of type 1 fimbriae in Escherichia coli autoflocculation
Authors: Goochee Charles F. , Hatch Randolph T. , Cadman Theodore W.
Published: December 2004

Techniques are reviewed for the identification and enrichment of fimbriae‐positive and fimbriae‐negative Escherichia coli. Fimbriae‐positive E. coli were observed to form a semistable suspension of pH 7.0 which settled at a rate much slower than the fimbriae‐negative bacteria. Intense autoflocculation of fimbriae‐positive E. coli was noted at pH values below 5.2.
Enzymic interesterification of fats: Laboratory and pilot‐scale studies with immobilized lipase from Rhizopus arrhizus
Authors: Wisdom R. A. , Dunnill P. , Lilly M. D.
Published: December 2004

An immobilized lipase suitable for fat interesterification has been prepared by precipitation with acetone of a commercial lipase from Rhizopus arrhizus onto diatomaceous earth. As observed previously with a less active enzyme from Aspergillus sp., the interesterification activity was enhanced by addition of purified lipase or by high loadings of commercial enzyme. The interesterification activities reached maximum values in both cases. For immobilized preparations with purified enzyme, interesterification activity was also enhanced by the presence of a precoat of glutaraldehyde cross‐linked commercial lipase. A 2.9‐L column of immobilized lipase was used to interesterify batches of shea oleine (67 kg) and shea oil (40 kg). Little activity was lost processing shea oleine, but slow poisoning of the bed occurred when shea oil was fed to the column.
Geometrical design of immobilized cell modular units for ethanol fermentation
Authors: Bourassa Jean‐François , LeDuy Anh
Published: December 2004

Formula are developed for calculating the performance characteristics (surface‐to‐total‐volume ratio, surface‐to‐packing‐volume ratio, and void volume fraction) of four different types of immobilized cell modular units (ICMUs) for ethanol fermentation: plate‐type, spiral‐type, beehive‐type and bead‐type ICMUs. Examples are used to illustrate how the formulas are useful for investigating the effects of characteristic dimensions of packing geometry, as well as the effect of scale on the performance characteristics of the ICMUs.
Attachment and growth of mammalian cells on microcarriers with different ion exchange capacities
Authors: Himes Vaughn B. , Hu Wei‐Shou
Published: December 2004

In the design of microcarriers for animal cell growth, the exchange capacity has been considered a critical factor. However, charge densities of microcarriers under culture conditions are not the same as the exchange capacities. Furthermore, the charge density requirement for optimum attachment is not necessarily the same as that required for optimum growth. We demonstrate that charge is not the sole factor affecting the attachment and growth of animal cells on microcarriers. We also show that supplemental serum in the growth medium has a negative effect on cell attachment to microcarriers.
Growth kinetics of Eschericia coli containing temperature‐sensitive plasmid pOU140
Authors: Betenbaugh Michael J. , diPasquantonio Vincent M. , Dhurjati Prasad
Published: December 2004

The growth dynamics of Escherichia coli with the temperature‐sensitive plasmid, pOU140, were examined. Recombinant cells exhibited nearly identical kinetic behavior to host cells at low culture temperatures and low copy numbers. However, at higher temperatures, in which the copy number was significantly increased, the recombinant cells showed decreased stability along with lower growth rates and substrate yields as compared to the host. Furthermore, the production of a constitutive cloned‐gene protein was shown to increase with temperature in an Arrhenius fashion when culture temperature was varied between 38 and 42°C. These results suggest that temperature can be used to quantitatively control the production of a desirable plasmid‐coded gene product.
The electrochemical regeneration of NAD+ revisited
Authors: Laval Jean‐Marc , Bourdillon Christian , Moiroux Jacques
Published: December 2004

An actual yield of 99.97% (i.e., 3000 potential regenerating cycles) has been obtained for the electrochemical regeneration of NAD+. The deactivation of the coenzyme is not related to the number of cycles; it is only time dependent. For biotechnological applications, these results show that electrochemical regeneration can compete with enzymatic regeneration for selective oxidation by dehydrogenases.
Biomass retention and performance of anaerobic fixed‐film reactors treating acetic acid wastewater
Authors: Hamoda M. F. , Kennedy K. J.
Published: December 2004

An acetic‐acid‐based synthetic wastewater of different organic concentrations was successfully treated at 35°C in anaerobic downflow fixed‐film reactors operated at high organic loading rates and short hydraulic retention times (HRTs). Substrate removal and methane production rates close to theoretical values of complete volumetric chemical oxygen demand (COD) removal and maximum methane conversion were obtained. A high concentration of biofilm biomass was retained in the reactor. Steady‐state biofilm concentration increased with increased organic loading rate and decreased HRTs, reaching a maximum of 8.3 kg VFS/m3 at a loading rate of 17 kg COD/m3 day. Biofilm substrate utilization rates of up to 1.6 kg COD/kg VFS day were achieved. Soluble COD utilization rates at various COD concentrations can be described by half‐order reaction kinetics.
Adaptive steady‐state optimization of biomass productivity in continuous fermentors
Authors: Harmon Jeff , Svoronos Spyros A. , Lyberatos Gerasimos
Published: December 2004

An adaptive steady‐state optimization algorithm is presented and applied to the problem of optimizing the production of biomass in continuous fermentation processes. The algorithm requires no modeling information but is based on an on‐line identified linear model, locates the optimum dilution rate, and maintains the chemostat at its optimum operating condition at all times. The behavior of the algorithm is tested against a dynamic model of a chemostat that incorporates metabolic time delay, and it is shown that large disturbances in the subtrate feed concentration and the specific growth rate, causing a shift in the optimum, are handled well. The developed algorithm is also used to drive a methylotroph single‐cell production process to its optimum.
Factors affecting biomass attachment during startup and operation of anaerobic fluidized beds
Authors: Stronach Sandra M. , Diaz‐Baez Maria C. , Rudd Thomasine , Lester John N.
Published: December 2004

Three anaerobic fluidized bed reactors at 37°C were utilized to observe the effects of startup and operational procedures on biomass attachment. Using a meat‐based synthetic waste and stepped‐loading regime, the influences of synthetic polymer addition and maintenance of anaerobiosis during startup were investigated. Subsequently, increasing bed expansions were applied to assess shear effects. Synthetic polymer addition enhanced biomass retention but did not improve process performance. Maintenance of a reduced environment ameliorated fluctuating process parameters during start up and aided biomass retention and substrate removal. A bed expansion of 5% was detrimental to biomass attachment and COD removal but system stability was maintained at expansions between 10% and 30%. Startup was achieved in 56 days. Anaerobiosis appeared to enhance the initial evolution of a stable, well‐adapted microbial population, whereas polymer addition interfered with this. Moderate bed expansions had negligible effects on attachment and performance.
Oxygen transfer to mycelial fermentation broths in an airlift fermentor
Authors: Moo‐Young Murray , Halard Benoit , Allen D. Grant , Burrell Robert , Kawase Yoshinori
Published: December 2004

Oxygen transfer rates and gas holdups were measured in mycelial fermentation broths of Chaetomium cellulolyticum and Neurospora sitophila, each cultured in a 1300‐L pilot‐plant‐scale airlift fermentor. These cultures exhibited highly non‐Newtonian flow behavior coupled with a substantial decrease in oxygen transfer rates. The volumetric mass transfer coefficients in these cultures were found to be 65–70% lower than those in water. The data were compared with the available correlations obtained for simulated fermentation broths. In general, the data for C. cellulolyticum are in satisfactory agreement with the correlations for the model media but the data for N. sitophila are higher than that predicted by the correlations. Model media based correlations are found to be applicable to the fermentation processes if the culture medium does not possess a high yield stress.
Anaerobic digestion of wood ethanol stillage using upflow anaerobic sludge blanket reactor
Authors: Callander I. J. , Clark T. A. , McFarlane P. N.
Published: December 2004

The anaerobic digestion of wood ethanol stillage in a UASB reactor was studied. At organic loading rates be low 16 kg COD/m3 day the reactor performed effectively, achieving soluble COD and BOD removals in excess of 86 and 93%, respectively. Removal of color averaged 40%. At a loading rate of 16 kg COD/m3 day the methane yield was 0.302 L CH4 (STP)/g COD removed, and the observed cell yield was 0.112 g VSS/g COD removed. Operation of the reactor at higher loading rates was unsuccessful. Nitrogen, phosphorus, and alkalinity were supplemented. No additions of the essential trace elements Fe, Co, and Ni were required.
Economic assessment of plant cell culture for the production of ajmalicine
Authors: Drapeau D. , Blanch H. W. , Wilke C. R.
Published: December 2004

Cost estimates have been prepared for commercial‐scale production of ajmalicine‐rich Catnaranthus roseus biomass using plant cell culture. At the current state of the technology the cost would be approximately $7.30/lb dry biomass ($3215/kg ajmalicine). Naturally‐grown C. roseus roots have a 50% lower ajmalicine concentration but would cost only ca. $0.70/lb ($619/kg ajmalicine). The principal reason for the high cost of the plant cell culture route is not the slow specific growth rate (0.35 day−1), but rather the slow specific product accumulation rate (0.26 mg/g day). This rate will have to be increased by a factor of 40 to make the process competitive.
Concentration multiplicity in a draft tube fluidized‐bed bioreactor involving two limiting substrates
Authors: Tong C. C. , Fan Liang‐Shih
Published: December 2004

Concentration multiplicity in a two‐phase or three‐phase draft tube fluidized‐bed bioreactor containing biofloc particles is studied. The kinetics of biological reactions considered involve two limiting substrates. The necessary and sufficient conditions for concentration multiplicity in both the biofilm and bioreactor are examined in terms of effectiveness factor, inlet and bulk concentration of substrates, and liquid flow rate. Hysteresis behavior in both the biofilm and bioreactor and multiplicity of concentration profiles in the biofilm are also discussed.
Biomass photochemistry: XI. Photochemical pretreatment of cellulose and its fungal degradation
Authors: Durán Nelson , Rodríguez Jaime , Gómez Edgardo , Campos Victoriano , Baeza Jaime
Published: December 2004

In order to study the single‐cell proteins and cellulase production, fungal degradation of α‐cellulose was tested. Photochemical pretreatment of α‐cellulose at λ > 254 nm increases by over 100% the cellulase production by Chrysonilia sitophila (TFB strain). This is reflected in a larger production of soluble proteins in the filtrate with higher cellulase activity when compared with unirradiated cellulose. Single‐cell protein production (insoluble proteins) was also improved after preirradiation of cellulose or even on rice hull as the only carbon source after inoculation with the spore of C. sitophila. This pretreatment is a valuable method for increasing the digestibility of lignocellulosic materials.
Modeling and analysis of elution stage of biospecific adsorption in finite bath
Authors: Arve B. H. , Liapis A. I.
Published: December 2004

A model is developed and used to predict the dynamic behavior of the elution stage of biospecific adsorption (affinity chromatography) in a finite bath. Both nonselective and selective elution of monovalent adsorbates is considered. The model expressions account for film and pore diffusion resistances for the adsorbate(s) and the eluent, and various rate expressions for the desorption of the adsorbate from the adsorbate–ligand complex are constructed and studied. The results indicate that the duration of the elution stage depends significantly on the Sherwood number of the adsorbate and the rate of the interaction step between the ligand and the adsorbate relative to the diffusion of the adsorbate in the pore during elution. In nonselective elution, when the value of the effective pore diffusivity of the eluent is significantly larger than that of the adsorbate, the results suggest that it would be advantageous to use an initial eluent concentration in the finite bath that is only slightly higher than the critical eluent concentration in order to minimize the risk of product and ligand damage. In selective elution the amount of adsorbate recovered in the elution stage is greatly influenced by the initial concentration of the eluent and the equilibrium dissociation constants of the adsorbate–ligand and adsorbate–eluent complexes.
Kinetics of α‐amylase synthesis from Bacillus amyloliquefaciens
Authors: Yoo Young J. , Cadman Theodore W. , Hong Juan , Hatch Randolph T.
Published: December 2004

The microbial production of α‐amylase from Bacillus amyloliquefaciens was investigated. The microorganism was grown using media containing glucose or maltose at 37°C and under aerobic conditions in a 16‐L fermentor. The α‐amylase synthesis from maltose was not found to be inducible but was found to be subject to catabolite repression. The maltose uptake rate was observed to be the rate‐limiting step compared to the conversion rate of maltose to glucose by intracellular α‐glucosidase. The α‐amylase activity achieved with maltose as a substrate was higher than that achieved with glucose. A slower growth rate and a higher cell density were obtained with maltose. The enzyme production pattern depended upon the nutrient composition of the medium.
Improved performance of intensive semicontinuous cultures of Scenedesmus by biomass recirculation
Authors: de la Noüe J. , Ní Eidhin D.
Published: December 2004

The microscopic green alga, Scenedesmus obliquus, was used in a semicontinuous culture system for the tertiary treatment of urban wastewater, with the simultaneous production of usable biomass. Partial biomass recycling was used to increase the productivity of the system by overcoming the limits imposed by the low maximal growth rate of the alga. The biomass to be recycled was collected by simple gravity settling of the removed culture.

The culture system was operated at different dilution rates and its productivity measured at each rate. An evaluation of the crude nutrient composition of the algae produced at each dilution rate was also carried out.

The system was found to operate stably at dilution rates of up to 0.8 day−1 which represents a 20% net increase over the maximum dilution rate allowed under the same conditions in a system without recirculation. The composition of the biomass produced varied little over a range of dilution rates, which may be of relevance to its projected end‐use.

The study indicated that such a system can exploit available light to the full and should be of particular value for the treatment of low‐strength wastes such as we employed.