摘要:

AbstractA multivariable on‐line adaptive optimization algorithm using a bilevel forgetting factor method was developed and applied to a continuous baker's yeast culture in simulation and experimental studies to maximize the cellular productivity by manipulating the dilution rate and the temperature. The algorithm showed a good optimization speed and a good adaptability and reoptimization capability. The algorithm was able to stably maintain the process around the optimum point for an extended period of time. Two cases were investigated: an unconstrained and a constrained optimization. In the constrained optimization the ethanol concentration was used as an index for the baking quality of yeast cells. An equality constraint with a quadratic penalty was imposed on the ethanol concentration to keep its level close to a hypothetical “optimum” value. The developed algorithm was experimentally applied to a baker's yeast culture to demonstrate its validity. Only unconstrained optimization was carried out experimentally. A set of tuning parameter values was suggested after evaluating the results from several experimental runs. With those tuning parameter values the optimization took 50–90 h. At the attained steady state the dilution rate was 0.310 h−1the temperature 32.8°C, and the cellular productivity

ISSN:0006-3592    

DOI:10.1002/bit.260340502

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe physiology of lactate production byLactobacillus delbreuckiiNRRL B‐445 in a continuous fermenter with partial cell recycle has been studied and compared with that observed in a conventional chemostat. Partial cell recycle was achieved using a hollow‐fiber ultrafiltration cartridge. The biomass growth yield was reduced in the recycle fermenter while culture viability and the cellular content of polysaccharide, protein, carbon, and nitrogen remained constant, suggesting an enlarged specific rate of glucose consumption for nonanabolic (e.g., maintenance) functions. The volumetric productivity of lactate was enhanced in the recycle fermenter due to the complete utilization of glucose. The yield of lactate from biomass and the molar product ratio, lactate: ethanol plus acetate, decreased with increasing recycle ratio. Enhanced formation of ethanol and acetate occurred in the recycle fermenter although lactate remained the major product. The change in product profile was due to glucose limitation. The specific activity of lactate dehydrogenase remained constant during recycle fermentation. These physiological observations have implications for the future application of cell recycle to production proces

ISSN:0006-3592    

DOI:10.1002/bit.260340503

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractIt has been reported in the literature that several microbial species have a considerable sorption capacity for heavy metals. Work herein reported, accomplished using a heterogeneous microbial population developed in a modified extended aeration activated sludge process, indicates sorption capabilities as good as, or better than, those for individual microbial species. The process herein described may have several advantages over pure or controlled culture processes and it offers the possibility for reuse of organic matter needed to regenerate metal‐sorbing biomass, as well as autodigestion of excess biomass. The work also indicates that acclimation to high levels of a specific heavy metal (Cd) does not confer acclimation to another heavy metal (Cu

ISSN:0006-3592    

DOI:10.1002/bit.260340504

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractIn this article a two‐phase system for the continuous digestion of wastes with a high solid content is simulated. The studied parameters are: (1) Recirculation from the methanizer to the hydrolyzer, (2) methanizer/hydrolyzer volume ratio, and (3) hydraulic retention time in the hydrolyzer (HRT). Results show that the recirculation ratio is an important operational factor with a large influence on the biodegradation yield, especially at low HRT. Optimum levels of this parameter are established. Some runs of the program have been carried out to test the stability of the system. This has proved to be very stable, especially at low recirculation ratios. The results also show that volume ratio does not appreciably affect the performance of the system, provided it is over a critical value, dictated by the allowable methanizer loa

ISSN:0006-3592    

DOI:10.1002/bit.260340505

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractAerated and unaerated power consumption and flow patterns in a 0.56 m diameter agitated vessel containing water with dual Rushton turbines have been studied. Under unaerated conditions with a liquid height‐to‐diameter ratio of 2, an impeller spacing of 2 to 3 times the impeller is required for each to draw an amount of power equal to a single impeller. For aerated conditions, if a similar spacing is used, equations for the flooding‐loading transition and for power consumption for a single Rushton impeller can be extended relatively easily to dual systems. All results for this spacing are explained by reference to bulk flow patterns and gassed‐filled cavity structures and the proportion of sparged gas flowing through the upper impeller is also estimated. Such a spacing is generally recommended since it maximizes the power draw and hence the potential for oxygen mass transfer. Data are presented for other spacings but the results do not fit in easily with single agitator studies because strong impeller‐impeller flow pattern interacti

ISSN:0006-3592    

DOI:10.1002/bit.260340506

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractRecycle unit operations for suspension cell cultures may be improved by flocculation of the cells. A flocculant search was conducted, and it was found that where strongly cationic polymers were severly toxic to the cells, neutral and anionic polymers were nontoxic and ineffective at flocculating the cells. A weak and poorly soluble polycation, poly‐L‐histidine, was capable of flocculating cultures of CHO, HeLa, U‐937, and CRL 1606 hybridoma cells with no toxicity to the majority of cells. In addition to the lowered acute toxicity, the polymer treatment left the cells in a growing state for recycle. Flocculation was found to be mediated by precipitates of the polymer. The low toxicity of poly‐L‐histidine is probably due to its low solubility and charge at physiological pH. Nonelectrostatic interactions may also pl

ISSN:0006-3592    

DOI:10.1002/bit.260340507

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe antiviral activity of a surface‐bonded quaternary ammonium chloride (QAC) was examined in this study. The mechanism of inactivation was elucidated by a combination of infectivity assay, radioactive labeling assay, and sedimentation analysis. Although the virions are still infectious when attached onto the chemically modified surface, we found these viruses are inactivated if they are eluted from the surface. The inactivation is caused by the disruption of the viral envelope with subsequent release of the nucleocapsid. No evidence indicates the released nucleocapsid is further disrupted. An enveloped virus shows a much higher affinity for the QAC‐treated surface than a nonenveloped one due to hydrophobic interaction. The QAC‐treated beads can effectively remove the enveloped viruses at low protein concentrations. The titer of herpes simplex virus was reduced by a factor of nearly 5 logarithm units in a 0.5 wt % bovine serum albumin solution with less that 10% protein loss. However, the presence of proteins in the solution reduced both the rate and capacity of this nonspecific adsorption–inactivation process. As a consequence, the removal efficiency is relatively poor in solutions with high protein

ISSN:0006-3592    

DOI:10.1002/bit.260340508

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractAn algorithm is presented for detecting the appearance of contaminants during batch or fed‐batch fermentations, using only presently available on‐line measurements. Its adaptive nature enables it to rely on almost no prior knowledge of the real process. The necessary on‐line measurements are total biomass and its production rate; it is also shown how a physical variable such as oxygen uptake can be used alone instead. The algorithm's properties are studied theoretically and through simulations. These were confirmed by on‐line experimental results, obtained with a Yeast culture, both pure and contaminated by a Bacteria. The algorithm does not detect contaminants when none are there, and it also provides a convergent estimate of a pure culture's specific growth rate. Contaminated cultures are recognized by the algorithm, and this detection can be made more or less conservative. After detection, the various estimates may diverge, due to general observability difficulties, though this divergence can itself be monitored. Moreover, the algorithm is easy to tune and its qualitative behavior is quite insensitive to its adjustable parameters. A practical criterion and scheme for implementation are proposed. The generality of the approach, which far exceeds the experimental system used, is finally di

ISSN:0006-3592    

DOI:10.1002/bit.260340509

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractModel experiments were performed with starved yeast (Saccharomyces cerevisiae) cultures in a batch reactor in order to develop a better understanding of NAD(P)H and flavin culture fluorescence. Fluorescence was monitored during aerobic–anaerobic–aerobic transitions and ethanol and glucose substrate addition experiments. Interpretations of the fluorescence responses obtained are provided, with consideration given to redox compartmentation and the formation of ethanol shortly after a glucose addition. An analytical spectrofluorophotometer was interfaced to a personal computer and adapted to measure fluorescence in a bioreactor. This was achieved by the use of quartz fiber‐optic waveguides to convert the right‐angle cuvette geometry of the analytical spectrofluorophotometer to an open‐ended fluorescence probe geometry, resulting in a flexible culture fluorescence apparatus. Features of the apparatus include variable excitation and emission wavelengths, allowing for detection of NAD(P)H or flavin fluorescence, as well as small slit widths, a variable sampling rate, excitation and emission scanning capabilities, and good se

ISSN:0006-3592    

DOI:10.1002/bit.260340510

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractMeasurements of mass transfer in a highly viscous pseudoplastic broth, which is typical toXanthomonas campestrisfermentations, are difficult to obtain by conventional methods and little data is available. A novel research method that uses bioluminescence for mass transfer studies has been developed. A plasmid carrying the luminescence operon of marine luminous bacteria is introduced into an industrial bacteria,X. campestris.Besides producing the polysaccharide xanthangum, the bioluminescentX. campestrisemits measurable light. Monitoring the luminescence is a simple, noncontaminating nondestructive and very sensitive indicator of the metabolic activity of the culture during fermentation. Energy drain due to bioluminescence is very low; growth rate and polysaccharide production rate are close to those of the wild‐type strain.Oxygen and substrate mass transfer are determined by inducing step or periodic fluctuations in their concentration and measuring the resultant luminescence response. Oxygen mass transfer coefficients show linear dependence on Reynolds number and an exponential dependence on the average shear rate. Viscosity effect is small at high viscosities but increases rapidly below 10 Pa‐s. The influence of oxygen uptake rate is studied.Mass transfer of the limiting component (ammonium ions) is analyzed under pulsating feed conditions. The luminescence declines, following a feed pulse, due to energy investment in active transport of ammonium ions through the cell membrane, it regenerates then to its baseline. The relation between mass transfer and luminescence fluctuation is elucida

ISSN:0006-3592    

DOI:10.1002/bit.260340511

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY