Bed Of Beads Research Articles

Cell–cell and cell–surface interactions in an illuminated biofilm: Implications for marine sediment stabilization†

Most wetted surfaces that are illuminated support a population of phototrophs. The marine sediment is no exception and there the major component of the microphytobenthic population is diatoms. These organisms are credited with stabilizing the sediment against physical disturbance by virtue of the extracellular carbohydrate polymers that they elaborate. However, diatoms synthesize and secrete several carbohydrate polymers and it is not certain which of them is involved in the stabilization process. In order to investigate this, we have constructed small glass bead-filled flow through bioreactors to mimic marine sediments. The flow rate through the bioreactors was found to reflect the physical stability of the bead bed. Thus flow rate was measured as a function of diatom growth and the production of three operationally-defined polymers, i.e., those soluble in the medium, those soluble in 0.5 M NaHCO3 at 90 °C and those not soluble in either solvent (matrix polymer). Growth of the diatoms did not change the hydraulic conductivity of the bioreactors. For Amphora coffeaeformis, neither did the production of medium-soluble nor NaHCO3-soluble polymers. However, matrix polymer accumulation was directly correlated with a reduction in flow (regression coefficient R2 = 0.96) and stabilization against physical disturbance. Results with species of Navicula were not as clear. Both NaHCO3-soluble and matrix polymers were involved in producing the flow reduction. In the same manner we also measured the effect of Pseudoalteromonas haloplanktis growth on bead bed hydraulic conductivity and bead bed stability. Growing alone, no effect was found, but in co-culture with a single diatom species, the bacteria reduced the diatom effect on flow through the bioreactors seen earlier, however did not reduce the extent of their growth. Confocal scanning laser microscopy of beads colonized with diatoms alone, or diatoms in co-culture with bacteria, revealed that P. haloplanktis was able to inhibit diatom adhesion to the beads. When the bacteria were present there was less matrix polymer evident. We speculate that this interference with diatom metabolic activity was either the result of less matrix polymer synthesis, or its hydrolysis by the bacteria. The results are applicable to mixed species biofilms of this type on surfaces other than sediments.

A NUMERICAL AND EXPERIMENTAL STUDY OF MICROWAVE DRYING USING A RECTANGULAR WAVE GUIDE

The drying of a capillary porous packed bed of glass beads by microwave energy using a rectangular wave-guide was investigated numerically and experimentally. The effects of moisture content, particle size and microwave power level on the drying kinetics were examined. Most importantly, this work focuses on the prediction of the distribution of the electromagnetic field as well as the temperature and moisture distribution within the capillary porous medium. The model, which combines the electromagnetic, temperature, and moisture fields, predicted results which were in good agreement with the experimental data.

PERFORMANCE CHARACTERISTICS OF THE VIBRATED FLUID BED OF INERT PARTICLES FOR DRYING OF LIQUID FEEDS

Experimental studies are presented on drying of soybean milk in a vibrated fluidized bed of inert particles. The effects of inlet air temperature, superficial air velocity, static bed height, and the feed rate on the bed pressure drop, product hold-up and the convective heat transfer coefficient are discussed. The thermal efficiency of the dryer as well as some basic characteristics for the vibrated fluid bed of glass beads and Teflon pellets are given and compared to the ones for conventional fluid beds. A regression equation for the volumetric heat transfer coefficient is provided.

MRI velocity measurements of water flow in porous media containing astagnant immiscible liquid

To investigate the flow characteristics of water in a porous mediumwith a second, stagnant, immiscible liquid phase, we experimentally studiedflow of water through a bed of glass beads containing stagnant silicone oil.For imaging, two magnetic resonance imaging (MRI) techniques were used: thechemical shift imaging method and the phase-encoding method. Two-dimensionalimages both with and without the silicone oil showed that the water velocityprofiles drastically changed because the stagnant silicone oil changed thepore structure. Significant changes in flow were also confirmed by composingeleven two-dimensional images of velocity profiles to visualize thethree-dimensional flow path and the stagnant silicone oil distribution in theporous media. A statistical method was developed to clarify the relationbetween pore structure and fluid flow. This method showed that, when stagnantsilicone oil is present, but with the same net flow of water, the reduction inrate of flow from large, oil-blocked pores is compensated by an increase inrate of flow from the larger number of small pores.

Bed expansion in liquid–solid two-phase fluidized beds with Newtonian and non-Newtonian fluids over the wide range of Reynolds numbers

Bed expansion characteristics in Newtonian and non-Newtonian fluid–solid two-phase fluidized bed have been examined. Bed expansion measurements were carried out for a bed of glass beads fluidized in Newtonian liquids (water and glycerol solutions) and non-Newtonian liquids (aqueous solutions of carboxymethyl cellulose (CMC) and xanthan gum). Measurements of bed voidage covered a terminal particle Reynolds number from 8.14 to 3947 and a flow index in a power-law model from 1 to 0.625. The bed voidage increased with an increase in the superficial liquid velocity and the magnitude of the increase became smaller as particle size increased. Increase in viscous non-Newtonian flow behaviour resulted in an increase of the bed voidage. The generalized correlation for the bed voidage was developed for Newtonian and non-Newtonian liquid–solid two-phase systems by extending the correlation of the drag coefficient for single particles to multiparticle systems. The predictions for bed voidage were in reasonable agreement with the present experimental data and the data in the literature for Newtonian and non-Newtonian liquid–solid two-phase systems in the whole Reynolds number region.

Removal of mixtures of acetaldehyde and propionaldehyde from waste gas in packed column with immobilized activated sludge gel beads

The removal of mixed acetaldehyde and propionaldehyde as a model of the binary contaminants in waste gas was studied in the packed column containing the immobilized activated sludge gel beads together with the hollow plastic balls developed for the removal of a single aldehyde in the previous work. The rate of each aldehyde biodegradation by the gel beads in the aldehydes mixture was expressed by the Michaelis–Menten type rate equation with an inhibitory term due to the other coexistent aldehyde. The kinetic parameters involved were found to be the same as those determined previously for biodegradation of a single aldehyde. A model for prediction of removal of each aldehyde in the packed column was developed assuming that each aldehyde dissolved in the aqueous phase within the gel bead was biodegraded according to the above rate equation with no mass transfer effect. The packed column was stable and efficient for removal of the binary aldehydes mixture with a very low pressure drop for gas flow due to a reduced gel beads bed compaction by the hollow plastic balls. Removal of each aldehyde decreased with increasing the inlet aldehyde concentrations since each biodegradation rate itself approached asymptotically the maximum one with increase in each aldehyde concentration. The observed removals for each aldehyde in the aldehydes mixture agreed well with those calculated from the design equations developed. The contact efficiency of gel beads with the waste gas stream was estimated to be the same value of 0.24 as in the previous work, supporting that the efficiency was specific to the geometrical and physical properties of the packed column used.

Stability analysis of a pressure swing adsorption process

Hydrodynamic stability during advection combined with diffusion and adsorption of a binary gas mixture in porous media is considered in this work. The general framework is that of pressure swing adsorption (PSA) on beds of zeolite beads. The dispersion/adsorption problem is studied at Darcy's scale on a 1D porous column from a numerical point of view while complete time-periodic cycles are considered. The regular solution of the problem is first sought using a finite volume scheme and stability analysis is performed on this time-dependent solution. While instability evidence is shown on a direct 2D numerical simulation of the problem with pressure and concentration disturbances at the entrance of the column, the stability analysis is carried out in 1D by making use of the linear amplitude equation method. Results clearly show the stability conditions which are quite different depending on whether pressure or concentration disturbances are considered as initial conditions or maintained as boundary conditions at column entrance.

Design criteria for dense permeation-selective membranes for enantiomer separations

Dense enantioselective membranes can distinguish between two enantiomers by different mechanisms. At this moment, it is not clear which mechanism provides the best membranes for large-scale enantiomer separations. Therefore, we studied the design criteria for permeation-selective membranes combining literature data, experiments and model calculations. Literature data on dense permeation-selective membranes for enantiomer separation show that these membranes could be divided into two different classes: diffusion selective and sorption selective. Reviewing the literature on diffusion-selective membranes shows that these membranes have one main disadvantage: the inverse proportionality relation between the permeability and selectivity. This disadvantage is absent for sorption-selective membranes. As a model system, the diffusion of phenylalanine through a packed bed of polypropylene beads coated with N-dodecyl- l-hydroxyproline:Cu(II) was studied. The experiments showed that the material could selectively adsorb phenylalanine (Phe) with a selectivity ( d/ l) of 1.25. However, no permeation selectivity could be detected. With a dual sorption model these results could be interpreted. These model calculations showed that the permeation selectivity only approaches the intrinsic selectivity of the selector if the selectively adsorbed population is mobile and the non-selective permeation is minimized. Therefore, to our opinion more emphasis should be put on the development of sorption selective membranes.

Combining filtration and catalytic combustion in particulate traps for diesel exhaust treatment

Satisfying performance in Diesel soot abatement can be achieved by coupling ceramic-foam filters with carbon combustion catalysts. This paper focuses on the preparation, testing and the modelling of such reactors. A specific pilot plant, based on a conical fluidised bed of glass beads, used to disperse fixed parcels of Diesel soot into a given gas flow rate, was used to assess the pressure drop and the filtration efficiency of the foam traps as a function of the soot particle size, the soot load in the filter, as well as the superficial velocity. Then, several catalysts have been deposited into different traps, whose abatement performance was evaluated in a specific pilot plant where an acetylene burner was used to produce a soot-laden flue gas. High abatement efficiency (>80%), coupled with low-pressure drop across the trap (100 mmH 2 O) , has been obtained by using a catalyst based on Cs 4V 2O 7. A mathematical model is presented and validated using the experimental data obtained with catalytic and non-catalytic traps. The model agreement with the experimental data was good in both cases and particularly promising for design purposes.

Cell?cell and cell?surface interactions in an illuminated biofilm: Implications for marine sediment stabilizationPresented during the ACS Division of Geochemistry symposium ?Biogeochemical Consequences of Dynamic Interactions Between Benthic Fauna, Microbes and Aquatic Sediments?, San Diego, April 2001.

Most wetted surfaces that are illuminated support a population of phototrophs. The marine sediment is no exception and there the major component of the microphytobenthic population is diatoms. These organisms are credited with stabilizing the sediment against physical disturbance by virtue of the extracellular carbohydrate polymers that they elaborate. However, diatoms synthesize and secrete several carbohydrate polymers and it is not certain which of them is involved in the stabilization process. In order to investigate this, we have constructed small glass bead-filled flow through bioreactors to mimic marine sediments. The flow rate through the bioreactors was found to reflect the physical stability of the bead bed. Thus flow rate was measured as a function of diatom growth and the production of three operationally-defined polymers, i.e., those soluble in the medium, those soluble in 0.5 M NaHCO3 at 90 °C and those not soluble in either solvent (matrix polymer). Growth of the diatoms did not change the hydraulic conductivity of the bioreactors. For Amphora coffeaeformis, neither did the production of medium-soluble nor NaHCO3-soluble polymers. However, matrix polymer accumulation was directly correlated with a reduction in flow (regression coefficient R2 = 0.96) and stabilization against physical disturbance. Results with species of Navicula were not as clear. Both NaHCO3-soluble and matrix polymers were involved in producing the flow reduction. In the same manner we also measured the effect of Pseudoalteromonas haloplanktis growth on bead bed hydraulic conductivity and bead bed stability. Growing alone, no effect was found, but in co-culture with a single diatom species, the bacteria reduced the diatom effect on flow through the bioreactors seen earlier, however did not reduce the extent of their growth. Confocal scanning laser microscopy of beads colonized with diatoms alone, or diatoms in co-culture with bacteria, revealed that P. haloplanktis was able to inhibit diatom adhesion to the beads. When the bacteria were present there was less matrix polymer evident. We speculate that this interference with diatom metabolic activity was either the result of less matrix polymer synthesis, or its hydrolysis by the bacteria. The results are applicable to mixed species biofilms of this type on surfaces other than sediments.

Explosive dispersal of solid particles

Abstract. The rapid dispersal of inert solid particles due to the detonation of a heterogeneous explosive, consisting of a packed bed of steel beads saturated with a liquid explosive, has been investigated experimentally and numerically. Detonation of the spherical charge generates a blast wave followed by a complex supersonic gas-solid flow in which, in some cases, the beads catch up to and penetrate the leading shock front. The interplay between the particle dynamics and the blast wave propagation was investigated experimentally as a function of the particle size (100–925 $\mu$ m) and charge diameter (8.9–21.2 cm) with flash X-ray radiography and blast wave instrumentation. The flow topology during the dispersal process ranges from a dense granular flow to a dilute gas-solid flow. Difficulties in the modeling of the high-speed gas-solid flow are discussed, and a heuristic model for the equation of state for the solid flow is developed. This model is incorporated into the Eulerian two-phase fluid model of Baer and Nunziato (1986) and simulations are carried out. The results of this investigation indicate that the crossing of the particles through the shock front strongly depends on the charge geometry, the charge size and the material density of the particles. Moreover, there exists a particle size limit below which the particles cannot penetrate the shock for the range of charge sizes considered. Above this limit, the distance required for the particles to overtake the shock is not very sensitive to the particle size but remains sensitive to the particle material density. Overall, excellent agreement was observed between the experimental and computational results.

Immersion chilling and freezing of a porous medium

An experimental apparatus, putting one face of a water-saturated glass bead bed in contact with a high-concentration (23% NaCl) aqueous freezant (the other face being insulated against heat and mass transfer), was constructed to simultaneous study heat and mass transfer at the product/solution interface and within the product more closely than is possible in real foods. The selected flow allowed uniform heat treatment (a constant heat transfer coefficient) over a large part of the product. The apparatus was used to monitor three elements within the product: the temperature profiles, the NaCl concentration profiles for the liquid phase and the freezing and thawing fronts. The first results showed that a surface layer of a highly impregnated non-frozen product was present at the end of freezing. If the frozen product was left in contact with the refrigerating solution, progressive thawing occurred from the surface inwards; thawed layer thickness seemed to be a linear function of the square root of time.

The effect of tangential lubrication by bridge liquid on the behavior of agglomerating fluidized beds

Cohesiveness due to particle wetting often causes significant troubles in many industrial fluidized processes. There are two contributions for liquid bridge force, i.e. static force and dynamic force. The dynamic force due to viscosity in the tangential direction is called hydrodynamic lubrication. Lubrication is the reduction of intra-particle friction force by switching from solid–solid Coulomb friction to the fluid shear resistance of the liquid bridges between particles. In the present paper, simulations of a fluidized bed were carried out by taking into account the tangential lubrication effect. Experiments were carried out by using a 200-mm diameter three-dimensional bed of glass beads. Results are compared in terms of pressure fluctuation and bubbling behavior. With the lubrication effect, particles moved more actively in the whole region of the bed and became less adhesive to the wall, but pressure fluctuation did not change much.

Purification of alpha-amylase isoenzymes from Scytalidium thermophilum on a fluidized bed of alginate beads followed by concanavalin A-agarose column chromatography.

An alpha-amylase has been purified from the thermophilic fungus Scytalidium thermophilum. A ninefold purification was achieved in a single step using fluidized bed chromatography wherein alginate was used as the affinity matrix. There are at least two isoenzymes as shown by concanavalin A (Con A)-agarose column chromatography. The isoenzyme binding to Con A is stable for at least 3 h at 80 degrees C in the presence of calcium ions. The isoenzymes have similar molecular weights of around 45,000 Da as shown by SDS-PAGE analysis. The isoenzymes differ only slightly in their pH optima and temperature optima but the isoenzyme binding to Con A-agarose has slightly higher thermal stability.

Short Reports

This short report describes the care of an extensive wound in a terminally ill patient and specifically draws attention to the role of the Oasis Fluidized Bead Bed (Figure 1) (Huntleigh Healthcare) in promoting the healing process and patient comfort.

Dynamics of Silica Colloid Deposition and Release in Packed Beds of Aminosilane-Modified Glass Beads

The transport and deposition dynamics of colloidal particles in packed porous media were investigated. The colloids were negatively charged silica particles (0.1 and 0.3 μm in diameter), and the packed-bed columns comprised aminosilane-modified glass beads. The glass beads acquired a positive surface charge by anhydrous chemical reaction with aminoethyl(N-aminopropyl)dimethoxymethylsilane. Maximum attainable surface-coverage (θmax) and excluded-area-parameter (β) values were determined for particle deposition experiments under various physicochemical conditions, namely, solution ionic strength, flow velocity, and particle size. The results demonstrated that excluded-area-parameter values increased with decreasing ionic strength and increasing flow velocity and particle size. Observed excluded-area-parameter values smaller than 1.83, the hard-sphere jamming limit according to random-sequential-adsorption (RSA) mechanics, alluded to the occurrence of multilayer deposition. The release of deposited particles after complete breakthrough was also investigated by reducing the ionic strength of the solution and by reversing the collector surface charge with an anionic surfactant (sodium dodecyl sulfate). Because colloid release was predominantly observed following deposition runs with higher values of surface coverage, which suggested the possible presence of multilayer deposition, it could be inferred that particle−particle repulsion was mainly responsible for the observed colloid release.

Heat transfer in fixed bed: a model non-linearity approach

Studies have been carried out on the heat transfer in a packed bed of glass beads percolated by air at moderate flow rates. Rigorous statistic analysis of the experimental data was carried out and the traditional two parameter model was used to represent them. The parameters estimated were the effective radial thermal conductivity, k, and the wall coefficient, h, through the least squares method. The results were evaluated as to the boundary bed inlet temperature, T 0, number of terms of the solution series and number of experimental points used in the estimate. Results indicated that a small difference in T 0 was sufficient to promote great modifications in the estimated parameters and in the statistical properties of the model. The use of replicas at points of high parametric information of the model improved the results, although analysis of the residuals has resulted in the rejection of this alternative. In order to evaluate non-linearity of the model, Bates and Watts (1988) curvature measurements and the Box (1971) biases of the coefficients were calculated. The intrinsic curvatures of the model (IN) tend to be concentrated at low bed heights and those due to parameter effects (PE) are spread all over the bed. The Box biases indicated both parameters as responsible for the curvatures PE, h being somewhat more problematic.

Two-dimensional nuclear magnetic resonance measurements and numerical simulations of fluid transport in porous rocks

Pulsed magnetic field gradient nuclear magnetic resonance (PFG-NMR) measurements have been performed for water flowing through porous Fontainebleau sandstones and are compared with flow through a packed bed of monodisperse glass beads. Pulsed gradients were applied both parallel (Z) and perpendicular (X) to the main flow axis simultaneously to obtain the two-dimensional displacement joint probability density PΔ(X,Z) of the moving spins. The evolution of PΔ(X,Z) as a function of encoding time Δ and flow rate Q is investigated. Good agreement is found between experimental PΔ(X,Z) and those obtained by numerical simulations of flow through computer-generated structures of equivalent statistical properties to those studied. The simulations are employed to compare a wider range of flow parameters than those accessible by experiment. In addition to averaged quantities, such as dispersion coefficients and moments of displacement distributions, the correlations between displacements in both directions are presented. The average transverse dispersion, 〈X2〉, for a subset of particles possessing a given axial displacement, Z, at any encoding time Δ is found to scale with Z; for flow rates and times discussed in this study, a power law relation 〈X2〉∝Zγ is observed with the spreading exponent γ being characteristic of the connectivity and statistical geometric features of the pore space. The correlation coefficient ρX2,Z is found to be positive in all cases and strongly influenced by the ratio of convective to diffusive contributions to the total particle displacements, expressed by the Péclet number. A maximum in the correlation coefficient occurs at a time scale dependent on the Péclet number and in the structures studied here, this corresponds to a characteristic lengthscale of the systems, approximated by their average pore size.

フラクタル次元を用いた２次元流動層の画像解析

Two-dimensional fluidized beds of glass and polystyrene beads were investigated from the view point of image analysis. Images of a two-dimensional fluidized bed were recorded by a digital video camera at 1/30-second intervals and the fractal dimension of a contour image was quantitatively determined by using the cover method. The fractal dimension fluctuates with time, corresponding to the birth, growth and collapse of bubbles in the fluidized bed. Fifty percent value and standard deviation of fractal dimension distribution increase with non-dimensional air velocity. The 50% value is correlated with a standard deviation of fractal dimension.

Continuous production of antibiotics in an airlift fermentor utilizing a transverse magnetic field.

In this study, a series of experiments was conducted to demonstrate the feasibility of continuous production of penicillin antibiotic using a three-phase magneto airlift fermentor with immobilized Penicillium chrysogenum. The fermentation processes were carried out in a 2.4-L external loop airlift utilizing a transverse magnetic field. It was found that the application of the magnetic field to a bed of ferromagnetic beads affects both the hydrodynamics of the reactor and the rate of the bioconversion process occurring inside it. One hundred hours after startup, the maximum penicillin concentration increased 48% as the magnetic field intensity increased from 0 to 35 mT, owing to the increased residence time of the substrate in the riser and the positive effect of the magnetic field on the effective fluid-solid interfacial area. In addition, the detached biomass concentration in the liquid phase was found to be only 5% of the immobilized biomass, owing to low shear levels and the absence of friction among the solid-phase particles.