Abstract: BACKGROUND: Dyes used in textile industries and released to their wastewaters are serious ecological problems as they are hard to degrade by common means used in wastewater treatment plants. White-rot fungi can biodegrade textile dyestuffs using their extracellular enzyme system. However, it is difficult to keep them in functional form in conventional wastewater treatment systems, because of their specific nutritional and physiological requirements. Selection of a suitable bioreactor type and mode of operation are crucial for successful implementation of white rot fungi in waste water treatment processes. RESULTS: Both Remazol Brilliant Blue R (RBBR) and Reactive Orange 16 (RO16) were decolorized efficiently in the trickle-bed reactor. A degree of decolorization exceeding 80% was achieved within 2 days with all mycelium carriers and both dyes. In reactors packed with plastic kitchen scourers and luffa sponge slices the decolorization degree reached 90% within 2 days. The initial rate of decolorization of RBBR dye was notably higher than the rate of 8016 decolorization. The lowest liquid hold-up value (1-1.5%) was achieved in the reactor packed with the plastic kitchen scourers, the largest hold-up value (3-5%) was observed in the reactor filled with luffa sponge. The longest mean retention time, 430 s, was achieved in the reactor with the luffa carrier at a liquid flow rate of 6.81 cm(3) min(-1); the shortest mean retention times (10-20 s) were achieved in the reactor filled with the plastic kitchen scourers. Broad liquid residence time distributions were observed in tracer experiments at all volumetric flow rates. CONCLUSIONS: The ability of I. lacteus to secrete laccase and manganese peroxidase enzymes in a trickle-bed bioreactor with three mycelium carriers was proved and quantified experimentally. The decolorization capability of the I. lacteus mycelium was only marginally influenced by the kind of carrier used. Basic operational characteristics of the reactor - residence times, axial dispersion and liquid hold-up - were determined at various liquid flow rates.(C) 2009 Society of Chemical Industry
Abstract: Penicillin G (PenG) (0.05 mol dm(-3) in phosphate buffer, pH = 8) was hydrolyzed in a continuous flow-through electro-membrane reactor (EMR) with the penicillin G acylase (PGA) (EC 3.5.1.11) immobilized in 10% (w/v) polyacrylamide membrane with an area of 900 mm(2), thickness of 1 mm and enzyme activity of 100 U cm(-3) and 160 U cm(-3), respectively. The PenG was continuously fed to the substrate compartment adjacent to one membrane surface. Reaction products were washed from the membrane by a phosphate buffer solution fed to the product compartment adjacent to the other membrane surface. The mean residence time of both streams was varied from 11.3 min to 45 min. An electric field perpendicular to the membrane surface was imposed on the reactor and the electric current density was varied from 0 to 822 A m(-2). Substrate conversion was determined as a function of the mean residence time, of the applied electric current density and of the enzyme activity of the membrane. The conversion increased with increasing residence time. The applied electric current increased substrate conversion by 200% at short residence times and at low enzyme activity of the membrane. Oscillatory reaction regime was evoked by step change of the mean residence time of reactant streams in the reactor. (C) 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
Abstract: Chaotic features of the macro-instability (MI) of flow patterns in stirred tanks are studied in this paper. Datasets obtained by measuring the axial component of the fluid velocity and the tangential force affecting the baffles are used. Two geometrically identical, flat-bottomed cylindrical mixing tanks ( diameter of 0.3 m) stirred with either pitched blade turbine impellers or Rushton turbine impeller are used in the experiments, and water and aqueous glycerol solutions are used as the working liquids. First, the presence of the MI component in the data is examined by spectral analysis. Then, the MI components are identified in the data using the proper orthogonal decomposition ( POD) technique. The attractors of the macro-instability are reconstructed using either the POD eigenmodes or a method of delays and finally the attractor invariants are evaluated. The dependence of the correlation dimension and maximum Lyapunov exponent on the vessel operational conditions is determined together with their distribution within the tank. No significant spatial variability of the correlation dimension value is observed. Its value is strongly influenced by impeller speed and by the vessel impeller geometry. More profound spatial distribution is displayed by the maximum Lyapunov exponent taking distinctly positive values. These two invariants, therefore, can be used to locate distinctive regions with qualitatively different MI dynamics within the stirred tank.
Abstract: Surface-enhanced Raman scattering (SERS) is a powerful technique of Raman signal detection of substances at a low concentration level. it allows observation of structural details of films with very small thicknesses. It is possible to achieve the enhancement of Raman signal of species located on the surface of properly prepared SERS-active substrates of up to ca 10(6). One of the main requirements for the substrate to be SERS-active is the proper roughness of the surface. In this work different SERS-active Au and Ag substrates suitable for spectral mapping were prepared using procedures which consisted of electrochemical deposition of metal layer and further roughening with oxidation-reduction cycles (ORC) treatment. The nanostructures of the metal surfaces were tested using atomic force microscopy (AFM). Monolayers formed both by covalent and noncovalent linkages to the metal surface were detected and Raman spectral maps were then measured. Roughening procedure of the substrates was optimized and its effect on the SERS enhancement was discussed. The relations among the surface nanostructure, optimal roughening, type of linkage of the analyte to the surface of the substrate and the Raman signal enhancement for the experimental conditions were studied. Copyright (C) 2008 John Wiley & Sons, Ltd.
Abstract: First results of an attempt to integrate an electro-membrane enzyme reactor with a fuel-cell stack in order to construct a multi-functional unit are presented. The experimental fuel-cell stack consists of nine single polymer electrolyte membrane fuel cells (with active cross-sectional area of 26cm(2)) consuming pure humidified hydrogen as the fuel. The stack is designed to deliver steady electric power of 30W (stack voltage of about 6V at current of about 5A). The electro-membrane enzyme reactor is composed of five flat-shaped compartments: the cathode and the anode compartments, two reactant stream compartments and the gel slab compartment. The active area of all the compartments is 9cm(2). The operating curves (current-voltage and power-current curves) of both sub-units and their dynamical behaviours have been measured over a wide range of operating conditions. A comparison of the operating curves of the fuel-cell stack and of the electro-membrane reactor confirmed that these subunits are electrically compatible and can be mutually integrated within a multi-functional unit, whilst the fuel-cell stack provides enough electrical energy to power also the necessary auxiliary equipment (pumps, blowers, etc.). (c) 2006 Elsevier B.V. All rights reserved.
Abstract: A mathematical model of an enzymatic separating microreactor with the electro-osmotic control of reaction component transport rates is analysed. The micro-reactor is considered in a form of a thin channel filled with a gel containing an immobilised enzyme and an adsorbent where the enzyme reaction, the molecular diffusion, the electro-osmotic flux and the adsorption take place. The substrate inhibited enzyme reaction splitting a non-ionic substrate to two non-ionic products is considered. The reactor operates in a periodic regime, when the channel entry is exposed to the periodic substrate concentration pulses. A chromatographic separation of reaction components, therefore, proceeds in the channel. Effects of principal operational parameters of the reactor system-the reaction channel length, the electric current density, the substrate inlet concentration, the rate of adsorption, and the enzyme activity-on resolution of the products at reactor outlet are analysed. The existence of optimum parameter values (maximising the resolution of reaction products) is shown and a multiparametric optimisation of the reactor performance is accomplished.
Abstract: This work is focused on mathematical modeling of reaction-transport processes in a microdevice for immunoassay. A mathematical model of a four-layer microdevice for a multiple enzyme-linked immunosorbent assay (ELISA) analysis in a serial configuration is proposed. Effects of electrokinetic transport and some significant parameters (e.g. antibody effective diffusivity/mobility, convective velocity, fixed charge in a porous membrane) on the immunoassay procedure are studied. The mathematical model includes component balances and Poisson equation of electrostatics. Steady-state analysis shows qualitative effects of the model parameters on the concentration of antibody in the reaction area. Dynamical analysis quantitatively reveals effects of crucial parameters on the time needed for the immunoassay procedure. It was observed that this time can be reduced to several minutes by a proper choice of control parameters. One complete step of ELISA application in the series arrangement of probes is analyzed in detail. (C) 2004 Elsevier B.V. All rights reserved.
Abstract: Experimental data obtained in a flat-bottomed cylindrical mixing vessel stirred with pitched blade impellers (four or six blades) or with a Rushton turbine impeller by measuring the tangential force affecting radial baffles are analysed. The presence of the macro-instability (MI) related component of the force was detected by spectral analysis of measured data. A single MI-related component occurring with a frequency of about 0.074N (N is the impeller speed) was detected for the pitched blade impellers. Two distinct frequencies, both directly proportional to the impeller speed, were detected for the Rushton turbine impeller: a lower frequency of approximately 0.025N and a higher frequency of about 0.085N. The upper frequency occurred only at low Re-M values. The lower frequency component occurred over the entire Rem range. The dimensionless frequencies were independent of the stirring speed, the vertical position along the baffle, the number of impeller blades, and liquid viscosity. The relative magnitude (k(MI)) of the MI-related component of the total force was evaluated by a combination of proper orthogonal decomposition (POD) and spectral analysis of experimental time series. The magnitude kMI varied in the interval from approximately 0.2 to 0.5. The dependence of the k(MI) on the impeller Reynolds number, the vertical position in the vessel, the number of impeller blades, the impeller off-bottom clearance and liquid properties is discussed.
Abstract: Penicillin G (2%, w/v in phosphate buffer, pH 8) was hydrolysed in a flow-through, miniature electro-membrane reactor with the penicillin G acylase immobilized in 5% (w/v) polyacrylamide (diam. 10 mm, thickness 2.6 mm, enzyme activity 24 U ml(-1)). The conversion of penicillin G increased from 0.15 to almost 0.5 when the electric current applied to the reactor was changed from -600 to + 600 A/m(2) with a substrate residency of 1 h.
Abstract: Penicillin G hydrolysis in a compartmentalised electro-membrane reactor with penicillin G acylase immobilised in a polyacrylamide gel Jab was studied. Penicillin G solution was fed to the substrate compartment stacked to one gel slab surface and reaction products were colleted in the product compartment adjacent to the other slab surface. An electric field perpendicular to the slab surface was imposed to the reactor by a couple of platinised titanium electrodes. The enzyme activity of the gel slab was varied from 30 to 150 U cm(-3) and density of the electric current passing through the slab (5% polyacrylamide, dimensions 40 mm x 40 turn x 2.7 mm) was varied from -1250 to +625 A m(-2). The current was considered as negative when electrophoretic migration augmented penicillin G transport from the substrate compartment to the product one. The reactor was operated in recirculation (batch) mode. The initial penicillin G concentration was 2% (w/v). Substantial increase of the rate of the penicillin G hydrolysis and of the volumetric slab productivity was observed both at negative and positive electric currents applied to the reactor. Fast replenishment of the consumed substrate was the reason of intra-slab reaction acceleration under the negative currents. The positive currents resulted to a close-to-optimum intra-slab pH value and consequent increase of the reaction rate. The positive currents, however, yielded only very poor separation of the reaction products from the unreacted substrate. Good separation was achieved when negative current of the density of -1250 A m(-2) was applied. The volumetric productivity of the slab at this current density was about 240 mol of the penicillin G hydrolysed per litre of the gel per one hour of reaction time. Temperature rise in the reactor due to the Joule heating was acceptable at all current densities. (C) 2003 Elsevier Inc. All rights reserved.
Abstract: A simple two compartment model system composed of a reservoir and a reactor is studied by means of numerical bifurcation analysis. An enzyme reaction involving ionic species is assumed to take place in the reactor connected to the reservoir via a semi-permeable electrically inert membrane. An external electric voltage is applied to this system via electrodes connected to each of the two compartments. An intra-membrane electric field caused by the applied voltage generates electrophoretic fluxes of each charged reaction component. We study the effects of a static and a periodically varying electric field on the dynamical regimes in the reactor. In the static case we find that a negative field supports the oscillatory dynamics while a positive field promotes multiplicity. Sinusoidal variations of the field cause a rich variety of dynamical responses, ranging from various periodic firing patterns to quasiperiodicity and chaos. These dynamical modes are associated with characteristic bifurcation structures in a forcing period - forcing amplitude bifurcation diagram which can be used for their classification.
Abstract: A model for the asymmetric coupling of two oscillatory cells is considered. The coupling between the cells is both through diffusional exchange (symmetric) and through the electromigration of ionic reactant species from one cell to the other (asymmetric) in applied electric fields. The kinetics in each cell are the same and based on the Gray-Scott scheme. Without the electric field, only simple, stable dynamics are seen. The effect of the asymmetry (applying electric fields) is to create a wide variety of stable dynamics, multistability, multiperiodic oscillations, quasiperiodicity and chaos being observed, this complexity in response being more prevalent at weaker coupling rates and at weaker field strengths. The results are obtained using a standard dynamical systems continuation program, though asymptotic results are obtained for strong coupling rates and strong electric fields. These are seen to agree well with the numerically determined values in the appropriate parameter regimes. (C) 2002 American Institute of Physics.
Abstract: Analysis of penicillin G hydrolysis in a membrane reactor with membrane-entrapped penicillin G acylase is performed using a mathematical model of the reactor system. An electric field imposed to the reactor is considered to enhance transport rates of reaction components and reaction rate. Diffusion, electrophoretic migration and electro-osmotic flux across the membrane are considered. The analysis focuses on possible effects of the principal operational parameters (electric field intensity, inlet substrate concentration, membrane thickness) on reactor performance. Multiplicities of steady states are frequently encountered. The membrane reactor performance can be easily targeted towards the required reaction regime by applying a constant or periodically varying electric field to the system. The periodic alternation of the polarity of the electric field substantially increases the effectiveness factor of penicillin hydrolysis compared with the steady state operation. Proper adjustments of electric field intensity may also compensate for the decay in enzyme activity. (C) 2001 Society of Chemical Industry.
Abstract: Effects of electro-transport processes in enzymatic reactors with spatially continuous unstirred reaction media (e.g., gels or polymers) on enzyme reactions are studied by numerical simulations. Two model enzyme reactions are chosen for analysis: (i) with no ionic reaction components, and (ii) with only ionic components and with production of H+ ions. The electrophoretic migration and electro-osmotic flux are considered as mechanisms altering transport rates of reaction components in unstirred reaction medium. Mathematical models of reactor system with hydrophilic membrane (or slab) containing immobilised enzyme with the DC electric field applied in a direction perpendicular to the membrane are constructed. Remarkable increase of the immobilised enzyme productivity was observed when the electric current of proper intensity was applied to the system. This optimum current value depends on substrate concentration, the slab thickness and the rate of enzyme inactivation. Main factor limiting applicability of the electric current to the reaction slab is heating of the slab due to the Joule heat. The electrophoretic migration of H+ ions in the second reaction system prevents local over-acidification, i.e. the averaged reaction yield is higher compared to the system with no electric field applied. An example of experimental results obtained in a laboratory-scale electro-membrane reactor with immobilised penicillin G acylase is also discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.
Abstract: A microreactor-separator system constructed of thin channel filled with an enzyme and microparticulate solid adsorbent immobilized in hydrophilic gel was studied by numerical simulations using a mathematical model of the reactor system. A substrate-inhibited enzyme reaction producing two nonionic products from nonionic substrate (e.g. sucrose hydrolysis by invertase) was considered. Electroosmotic flux and molecular diffusion were considered as mass-transport processes in the gel, as no electrophoretic migration was possible. The mathematical model involved the mass balances of all reaction components in liquid and solid phases, enthalpy balance, and equation describing the enzyme inactivation. A periodic switching of the substrate concentration at the reactor inlet, resulting in periodic alternation of reaction and separation periods, was applied. Dependences of the microreactor-separator operating measures (e.g. separation efficiency of the products) on basic operational parameters (switching period, electric current density, channel length, substrate inlet concentration) were analyzed.
Abstract: Results of the analysis of velocity data obtained by the laser Doppler velocimetry (LDV) in a flat-bottomed cylindrical stirred tank (300 mm diameter, filled with the liquid to the height equal to its diameter) equipped with four radial baffles and stirred with a pitch-blade turbine impeller are presented. Water and 85% aqueous glycerine solution were used as working fluids at three values of Reynolds number of the impeller: 75000, 1200 and 750. The fluid velocity was recorded in a rectangular region of evenly spaced points close to the stirrer region. The macro-instability (MI) of the velocity field was extracted from the experimental data using the proper orthogonal decomposition (POD) technique and spectral analysis. This approach enabled not only detection of the macro-instability in measured velocity data but also to quantify its relative magnitude (a ratio of kinetic energy captured by the macro-instability to total kinetic energy of the flow). The dependence of chaotic invariants of the MI on the Reynolds number and position of the measuring point in the vessel is constructed. The time evolution of the MI is reconstructed from experimental records. (C) 1999 Elsevier Science Ltd. All rights reserved.
Abstract: The conditions are established for the onset of convective instabilities in a general two-variable reaction-diffusion-advection system in which one of the reactant species is immobile. These results are applied in derail to predict the effects of applying electric fields in a model for cellular calcium wave propagation based on the calcium-induced calcium-release (CICR) mechanism. Extensive numerical simulations of this model are described and these show that spatial structures can be generated entirely through applying electric fields at the parameter values determined by the general theory. These structures take the form of propagating wave packets, and can be either relatively simple or have complex dynamics, depending on the kinetic parameters. (C) 2000 Elsevier Science B.V. All rights reserved.
Abstract: In this paper we examine dynamical modes resulting from diffusion-like interaction of two model biochemical cells. Kinetics in each of the cells is given by the ICC model of calcium ions in the cytosol. Constraints for one of the cells are set so that it is excitable. One of the constraints in the other cell-a fraction of activated cell surface receptors-is varied so that the dynamics in the cell is either excitable or oscillatory or a stable focus. The cells are interacting via mass transfer and dynamics of the coupled system are studied as two parameters are varied-the fraction of activated receptors and the coupling strength. We find that (i) the excitator-excitator interaction does not lead to oscillatory patterns, (ii) the oscillator-excitator interaction leads to alternating phase-locked periodic and quasiperiodic regimes, well known from oscillator-oscillator interactions; torus breaking bifurcation generates chaos when the coupling strength is in an intermediate range, (iii) the focus-excitator interaction generates compound oscillations arranged as period adding sequences alternating with chaotic windows; the transition to chaos is accompanied by period doublings and folding of branches of periodic orbits and is associated with a Shilnikov homoclinic orbit. The nature of spontaneous self-organized oscillations in the focus-excitator range is discussed. (C) 1999 American Institute of Physics. [S1054-1500(99)02201-6].
Abstract: Dynamical regimes arising due to mutual interactions of oscillatory and excitatory modes of the Belousov-Zhabotinskii (BZ) reaction in a two-array and linear and circular three-arrays (with different arrangements of intrinsic connections) of identical continuous stirred tank reactors (CSTRs) coupled via symmetric passive diffusion/convection mass exchange were studied both experimentally and by numerical simulations. The coupling strength among individual CSTRs and the threshold of excitability of the BZ reaction mixture were varied systematically. Firing numbers (vectors) were used for classification of observed oscillatory-excitatory modes. Full spectra of firing numbers ranging from 0 to 1 were detected in all CSTR arrays investigated in experiments. The numbers of oscillators and excitators, threshold of excitability, and the way of coupling and coupling strengths within the array are principal factors affecting firing patterns of the array, Numerical simulations with the dimensionless three-variable Oregonator based model of the BZ reaction predict qualitatively well dynamical regimes encountered in experiments. Noisy coupling among the individual CSTRs due to hydrodynamical fluctuations is suggested to explain some of the observed differences.
Abstract: Numerical analysis of dynamical regimes arising in reaction systems where an enzyme reaction with non-linear reaction kinetics, involving ionic reaction components, interacts with mass-transport processes is performed. Hydrolysis of the penicillins by means of the penicillin acylases is chosen as a model of enzymatic reaction system. It posseses highly nonlinear kinetics involving products inhibitions, hydrogen ions production and strong pH dependence of all kinetic parameters. It is further considered that the transport of all reaction components can be controlled by an electric field. First, a reactor system consisting of two stirred compartments separated by a diffusion barrier (the passive membrane) is studied. The enzymatic reaction takes place in the first compartment (the reactor) and the substrate is transported in and the products are transported out of the reactor through the membrane which connects the reactor to the second compartment (the reservoir) where concentrations of all reaction components are kept constant. The existence of multiple steady states, of sustained oscillations and of an excitability has been proved by numerical simulations of a mathematical model of the system. An application of observed dynamical regimes for construction of novel analytical tools is mentioned. Then another model system consisting of a planar membrane with the entrapped enzyme (the active membrane) immersed on both sides in the substrate and/or product solutions is studied. Not only diffusion but also an electrophoretic and electroosmotic transport of reaction components inside the active membrane, controlled by intensity of an electric field externally imposed across the membrane is considered. An effectiveness factor of the intramembrane enzymatic reaction is evaluated as a function of basic operational parameters of the system (extramembrane pH values, component concentrations, electric field intensity, transport parameters etc.) and of boundary conditions. Both, a significant increase and decrease of the effectiveness factor value due to the electric field applied to the system has been observed in numerical simulations. A precise tuning of the operational parameters is necessary in order to gain optimum performance of the active membrane system.
Abstract: Synchronizations of oscillatory regimes of the Belousov-Zhabotinskii (BZ) reaction in a circular array of three identical CSTRs coupled via symmetric passive diffusion/convection mass transfer were studied experimentally. Stability of symmetric and asymmetric phase-shifted oscillatory regimes with respect to variations of the coupling strength among the reaction cells was examined. The all-in-phase regime was found to be the only regime stable over the entire range of coupling strength values. Phase-shifted oscillatory regimes were found to be stable only within a narrow interval of very low coupling strength values. Spontaneous transitions of the phase-shifted regimes to the synchronized mode due to stochastic fluctuations of the coupling strength were observed. Numerical simulations with the four-variable Oregonator based model of the BZ reaction qualitatively confirmed the experimental findings. Propagation of an excitable response to periodic pulsed stimulations in a linear three-array of coupled chemical excitators (Belousov-Zhabotinskii reaction) was studied in dependence on the coupling strength, on the excitability level of the reaction mixture, and on the period and amplitude of pulse stimulation. Regimes of complete and partial propagation of the excitable response and the regimes of partial and complete propagation failure were observed. Numerical simulations predict qualitatively well excitatory regimes observed in experiments.
Abstract: The stability of periodic two-dimensional waves on a liquid film falling down a vertical oscillating plate was studied experimentally using the aqueous solutions of carboxymethylcellulose. A set of capacitance probes was used to measure the instantaneous film thickness. Artificial flow fluctuations induced by the plate oscillations caused distinct intensification of the wavy flow. We use the methods of phase space reconstruction and deterministic chaos analysis to show that the dynamics can be understood within the framework of deterministic chaos. We find that regions of relatively ordered and more complex chaotic dynamics alternate as the frequency of oscillations is varied. There are particular oscillating frequencies at which the system is close to a three-frequency quasiperiodic motion with the spectrum of Lyapunov exponents of type (0, 0, 0, -, ...), elsewhere the system is either in a simple chaotic mode with the spectrum of type (+, 0, 0, -, ...) or in a hyperchaotic mode with spectrum of type (+, +, 0, -, ...). (C) 1997 Elsevier Science Ltd.
Abstract: Recently developed stochastic model of a one-dimensional flow-through chemical reactor is extended in this paper also to the non-isothermal case. The model enables the evaluation of concentration and temperature profiles along the reactor. The results are compared with the commonly used one-dimensional dispersion model with Danckwerts' boundary conditions. The stochastic model also enables to evaluate a value of the segregation index.
Abstract: To the description of changes of solid particle size in population, the application was proposed of stochastic differential equations and diffusion equations adequate to them making it possible to express the development of these populations in time. Particular relations were derived for some particle size distributions in flow and batch equipments. It was shown that it is expedient to complement the population balances often used for the description of granular systems by a ''diffusion'' term making it possible to express the effects of random influences in the growth process and/or particle diminution.
Abstract: Some problems are analyzed arising when a numerical simulation of a random motion of a large ensemble of diffusing particles is used to approximate the solution of a one-dimensional diffusion equation. The particle motion is described by means of a stochastic differential equation. The problems emerging especially when the diffusion coefficient is a function of spatial coordinate are discussed. The possibility of simulation of various kinds of stochastic integral is demonstrated. It is shown that the application of standard numerical procedures commonly adopted for ordinary differential equations may lead to erroneous results when used for solution of stochastic differential equations. General conclusions are verified by numerical solution of three stochastic differential equations with different forms of the diffusion coefficient.
Abstract: Problems associated with the formulation of the boundary conditions for diffusion equations describing flow-through chemical-engineering systems from the point of view of stochastic process theory are discussed. An approach to modelling such systems is presented, allowing the one-dimensional diffusion (dispersion) model of a continuous flow mixer, commonly used in chemical engineering, to be reassessed from a rather general point of view.
Abstract: Formation of spatial inhomogeneities in the electric field intensity and charge density arising due to an interaction of diffusion or migration with chemical reaction in an ionic version of the Brusselator are presented. The model involving spatial variations of electric field is compared to a conventional model assuming spatially homogeneous electric field. Predictions of the effects of electric field on spatial patterns differ. The existence of the field induced transitions between stationary and oscillatory states in a one-dimensional system and between striped and hexagonal patterns in a two-dimensional system is demonstrated.
Abstract: A model of an isothermal one-dimensional continuous flow chemical reactor operating at the steady state was derived using a stochastic description of motion of the reacting molecules. The model enables evaluation of the conversion of the reacting components. At the limiting parameter values the model yields results identical to those of the simplified models conventionally used in chemical reactor engineering. The model also enables the applicability of Danckwerts' boundary conditions to be assessed from a more general point of view.
Abstract: The one-dimensional stochastic diffusion model of a continuous flow mixer is proposed incorporating (contrary to commonly used diffusion models) a distribution of velocities of diffusing particles. Simplifying assumptions enabled us to derive an analytical expression for the liquid residence time distribution and concentration profile inside the mixer. For extreme values of parameters, the model becomes identical with the common idealized models usually adopted in chemical engineering.
Abstract: A novel granular immobilized biocatalyst with invertase activity was prepared by mutual covalent bonding of native bakers' yeast cells Saccharomyces cerevisiae with polyethyleneimine and glutaraldehyde without the use of any solid carrier. The specific invertase activity of the biocatalyst was 300-1500 Ug-1. The optimum pH value for the invertase activity was 4.6. The half-life of the invertase activity was 500-1000 h at reaction temperatures of 60-75-degrees-C. The activation energy of sucrose hydrolysis equaled 36.2 +/- 5 kJ kmol-1 at reaction temperatures below 65-degrees-C. The enzyme reaction was inhibited by substrate at concentrations above 1.0-1.5 mol 1-1, depending on the particle size. The biocatalyst was used for batch sucrose hydrolysis in laboratory-scale reactors at substrate concentrations of 10-70% (w/w), pH 4.6, and temperatures of 60-75-degrees-C. The specific productivity of the biocatalyst was 3-10 h-1. The total biocatalyst productivity over the period of its lifetime was 2000-10,000 kg of sucrose hydrolysed per kilogram of the biocatalyst. The mechanical stability of the biocatalyst particles was quite satisfactory even during long-term operation in stirred reactors. The biocatalyst was stored at temperature +4-degrees-C for 1 year without appreciable loss of the invertase activity. The results of the biocatalyst exploration confirmed its applicability for enzymatic hydrolysis of even highly concentrated sucrose solutions under industrial conditions, especially at a high reaction temperature.
Abstract: An immobilized biocatalyst with invertase activity prepared by immobilization of whole yeast cells without use of any insoluble carrier was tested in tubular fixed-bed reactors from the point of view of possible application for continuous full-scale sucrose hydrolysis. At inlet sucrose concentration above 60% (w/w) and reaction temperature 60-70-degrees-C, total sucrose hydrolysis was achieved at a flow rate of 0.6-1.5 bed volumes per hour. At a flow rate about 10 bed volumes per hour, the conversion was still 0.5. The specific productivity of the biocatalyst was 3-25 h-1; the productivity of the reactor was 1-9 kg l-1 h-1. The half-life of the biocatalyst invertase activity was 815 h at 70-degrees-C. The specific pressure drop over the biocatalyst bed was less than 23 kPa m-1. The biocatalyst was proved to be fully capable of continuous sucrose hydrolysis in fixed-bed reactors.
Abstract: A process of segregation of two distinct fractions of solid particles in a rotating horizontal drum mixer was described by stochastic model assuming the segregation to be a diffusion process with varying diffusion coefficient. The model is based on description of motion of particles inside the mixer by means of a stochastic differential equation. Results of stochastic modelling were compared to the solution of the corresponding Kolmogorov equation and to results of earlier carried out experiments.
Abstract: The newly isolated Streptomyces sp. CCM 4102 strain produced a high level of intracellular glucose isomerase in the media containing D-xylose as inducer of the enzyme, corn-steep liquor, yeast extract and magnesium sulfate. The enzyme synthesis was repressed by D-glucose and D-fructose. The strain did not require cobalt ions for enzyme production.
