Acetate and ammonium diffusivity in membrane-aerated biofilms: improving model predictions using experimental results

2005 ◽  
Vol 52 (7) ◽  
pp. 121-126 ◽  
Author(s):  
J.W. Shanahan ◽  
A.C. Cole ◽  
M.J. Semmens ◽  
T.M. LaPara
Keyword(s):  
Population Stratification ◽  
Fluid Velocity ◽  
Effective Diffusivity ◽  
Substantial Variation ◽  
Biomass Density ◽  
Bacterial Populations ◽  
Modified Model ◽  
Biofilm Reactors ◽  
Model Predictions ◽  
High Fluid

Membrane-aerated biofilm reactors (MABRs) are advantageous for wastewater treatment because of their ability to achieve both nitrification and denitrification in a single bioreactor. The stratification of membrane aerated biofilms, however, needs to be better understood so that MABRs can be properly designed and implemented. In this study, we present a modified multi-population model that accounts for variation in effective diffusivity in biofilms of variable biomass density. For biofilms grown at a low fluid velocity (2 cm s−1), the variation in effective diffusivity had a profound effect on the predicted stratification and activity of bacterial populations. For biofilms grown at a high fluid velocity (14 cm s−1), biomass density was relatively constant as a function of depth and thus there was less substantial variation in effective diffusivity; our modified model, therefore, predicted a population stratification that was similar to its original version under these conditions.

Structure, Activity and Composition of Biofilms

1994 ◽  
Vol 29 (7) ◽  
pp. 335-344 ◽  
Author(s):  
Tian C. Zhang ◽  
Paul L. Bishop
Keyword(s):  
Dye Adsorption ◽  
Effective Diffusivity ◽  
Synthetic Wastewater ◽  
Bulk Solution ◽  
Plate Count ◽  
Spatial Distributions ◽  
Bacterial Populations ◽  
Surface Areas ◽  
Population Distributions ◽  
Micro Slicing

The spatial distributions of properties of biofilms have been investigated by using three different kinds of biofilms as test materials. Biofilms, cultured by laboratory-scale rotating drum biofilm reactors with synthetic wastewater, were first cut into 10 to 20 µm thick slices using a microtome, and then apportioned into samples representing 3 or 4 layers. The biofilm properties of each layer were investigated by measuring the densities, phospholipid concentrations, and AR18 dye adsorption abilities. The bacterial population distributions and the metabolically active bacterial distributions were studied by plate count methods or a MPN method, and the tetrazolium dye (INT) reduction method, respectively. Based on statistic evaluations, the micro-slicing technique, the procedure for analyzing phospholipid concentrations of biofilms, and the AR18 dye adsorption tests were suitable to be used in biofilm studies. It was found that the densities of biofilms in the bottom layers were 4 to 7 times higher than those in the top layers. For thick biofilms (thickness > 500 µm), the INT active bacteria decreased from 82-89% in the top layers to 5-11% in the bottom layers. The porosities of thick biofilms changed from 83-92% in the top layers to 56-64% in the bottom layers. For thin biofilms (thickness < 500 µm), the porosities of biofilms changed from 72-75% in the top layers to 35-44% in the bottom layers. Highly spatial distributions of bacterial populations, mean pore radius, and specific surface areas were also observed. As a result of these spatial distributions, the ratio of effective diffusivity to diffusivity in the bulk solution also shows a decrease with depth of the biofilm. Assuming biofilm properties are of a uniform distribution may be an over-simplified assumption, valid only in specific cases.

scholarly journals Measurement of local effective diffusivity in heterogeneous biofilms

1998 ◽  
Vol 38 (8-9) ◽  
pp. 171-178 ◽  
Author(s):  
H. Beyenal ◽  
A. Tanyolaç ◽  
Z. Lewandowski
Keyword(s):  
Flow Velocity ◽  
Liquid Flow ◽  
Empirical Equation ◽  
Effective Diffusivity ◽  
Mixed Population ◽  
Limiting Current ◽  
Biomass Density ◽  
Fast Evaluation ◽  
Novel Technique ◽  
Electroactive Species

We have developed a novel technique to measure local effective diffusivity distribution in heterogeneous biofilms. Mobile microelectrodes (tip diameter 10 μm) and the limiting current technique were employed to measure the effective diffusivity of electroactive species introduced to natural and artificial biofilms. We calibrated the microelectrodes in artificial biofilms of known effective diffusivity and known density. In mixed population biofilms, local effective diffusivity varied from one location to another and decreased toward the bottom of the biofilm. We related local effective diffusivity to local biofilm density using an empirical equation. Surface-averaged biomass density depended on liquid flow velocity at which the biofilms were grown. The higher the flow velocity, the denser were the biofilms. Our technique permits fast evaluation of local effective diffusivity and biofilm density in heterogeneous biofilms.

The effective long-time diffusivity for a passive scalar in a Gaussian model fluid flow

1978 ◽  
Vol 89 (2) ◽  
pp. 241-250 ◽  
Author(s):  
R. Phythian ◽  
W. D. Curtis
Keyword(s):  
Diffusion Processes ◽  
Fluid Velocity ◽  
Gaussian Model ◽  
Effective Diffusivity ◽  
Passive Scalar ◽  
Random Motion ◽  
Velocity Correlation ◽  
Molecular Diffusivity ◽  
Velocity Correlation Function ◽  
Long Time

The problem considered is the diffusion of a passive scalar in a ‘fluid’ in random motion when the fluid velocity field is Gaussian and statistically homogeneous, isotropic and stationary. A self-consistent expansion for the effective long-time diffusivity is obtained and the approximations derived from this series by retaining up to three terms are explicitly calculated for simple idealized forms of the velocity correlation function for which numerical simulations are available for comparison for zero molecular diffusivity. The dependence of the effective diffusivity on the molecular diffusivity is determined within this idealization. The results support Saffman's contention that the molecular and turbulent diffusion processes interfere destructively, in the sense that the total effective diffusivity about a fixed point is less than that which would be obtained if the two diffusion processes acted independently.

Fluid Dispersion and Distribution in Porous Media Using the Frequency Response Method With a Radioactive Tracer

1966 ◽  
Vol 6 (02) ◽  
pp. 143-152 ◽  
Author(s):  
R.R. Goddard
Keyword(s):  
Porous Medium ◽  
Phase Velocity ◽  
Frequency Response ◽  
Fluid Velocity ◽  
Effective Diffusivity ◽  
Radioactive Tracer ◽  
Dead End ◽  
Frequency Response Method ◽  
Response Method ◽  
The Waves

Abstract By use of the frequency response method with a radioactive tracer, it was possible to determine fluid dispersion and distribution in a natural consolidated and an unconsolidated medium. Measurements were made in a linear flow system at oleic saturations of 69 per cent in the consolidated medium, and 100 per cent in both media. Dispersion and distribution were obtained by measuring the amplitude attenuation and the phase velocity of sinusoidal waves with a dual monitor apparatus. The gamma ray emissions permitted in situ measurements at any distance along the porous samples. One result of importance was that the effective diffusivity increased as the wave length increased. As a consequence, a dispersion coefficient appropriate for the injection of large slugs might exceed the value measured by use of small slugs. Since flow models based solely on fluid velocity and an effective diffusivity coefficient imply that the diffusivity should be independent of frequency, such representations were not adequate for the data of this study. A comparison was made with a capacitance model of porous media with dead-end PV's, but even this model was not completely adequate. By using attenuation and phase velocity data, fluid dispersion can be predicted without postulating a differential equation satisfied by the tracer concentration, thereby eliminating the need of a complicated model to represent dispersion. Introduction The flow of similar miscible fluids through a porous medium can be fairly adequately described by two parameters: the average fluid velocity and the effective diffusivity.1-3 It has been pointed out recently, however, that significant discrepancies exist between this representation and the experimental data.4-7 An improved agreement can be obtained by introducing additional parameters based on the concept of dead-end pores. The purpose of the present investigation was to find out whether the frequency response method could be used to measure the relevant parameters. The method was used in the following form. A stream of fluid was flowed at a constant rate through a sample of porous material and the concentration of a radioactive tracer in the fluid was varied sinusoidally at a fixed frequency. The effects of flow through a porous medium are a decrease in the amplitude of the concentration wave and an increase in the velocity of the peaks of the waves above the average velocity. Attenuation and phase velocity of the waves were measured as a function of frequency and fluid velocity. The simple two-parameter model implies that the diffusivity should be independent of frequency. Data reported in this paper show that the diffusivity decreases as the frequency increases. Hence, as shown also by many others, the two-parameter model is not completely adequate. Coats and Smith5 used two additional parameters in their model: the volume of the dead-end pores and the rate of mass transfer between dead-end pores and the flowing stream. Their capacitance model of a porous medium containing some stagnant fluid, to which transfer occurs by molecular diffusion, did not explain the dispersion results of either the present study or of theirs. Instead, the capacitance effect can be better described as the result of extreme velocity variations within the pores of the medium, with transfer between the velocity zones by convection.

Research on Creep-Fatigue Life Prediction for P92 Steel under Stress-Controlled State

2013 ◽  
Vol 860-863 ◽  
pp. 972-977 ◽  
Author(s):  
De Xian Wang ◽  
Dong Mei Ji ◽  
Jian Xing Ren
Keyword(s):  
Experimental Data ◽  
Life Prediction ◽  
Fatigue Life Prediction ◽  
Effective Coefficient ◽  
P92 Steel ◽  
Modified Model ◽  
Model Predictions ◽  
Creep Fatigue ◽  
Prediction Capability ◽  
Life Prediction Model

Taking the P92 steel as the object,Creep-Fatigue (CF) tests of P92 steel at 873K under stress-controlled were carried out with GWT2504 equipment to investigate the CF life prediction. The life prediction model based on Applied Mechanical Work Density (AMWD) was developed in this study,and introduce the effective coefficient ƞ to modify the former. To verify the prediction capability of the AMWD-based and the modified model, comparisons of the models predicted lives with the experimental data of CF tests on P92 steel at 873K were made, it is found out that the AMWD-based model predictions for CF are in agreement with the experimental lives with the factors of 0.9013 and 1.0600, which verifies the model has a good predictability, and the Modified model with the factors of 0.9558 and 1.0469.

Pressure Drops and Model Modification for Two-Phase Flow in Porous Beds With Coarse Particles

2017 ◽  
Author(s):  
Xumao Zou ◽  
Liangxing Li ◽  
Liubo Kong ◽  
Huasheng Wang
Keyword(s):  
Two Phase Flow ◽  
Fluid Velocity ◽  
Experimental Studies ◽  
Test Facility ◽  
Phase Flow ◽  
Coarse Particles ◽  
Two Phase ◽  
Modified Model ◽  
Pressure Drops ◽  
Interfacial Drag

Motivated by reducing the uncertainties in coolability analysis of a debris bed, this paper proposed a modified model for the pressure drops of two phase flow through packed beds with coarse particles based on the experimental studies. The experiments are carried out on the test facility of DEBECO-LT (DEbris BEd COolability-Low Temperature), which was designed to investigate single / two-phase flow in porous beds. The coarse particles are packed in the cylindrical test section with the inner diameter of 120 mm and the height of 600 mm. Through single-phase flow tests in homogeneous beds, the reliability of the whole experimental system is ensured. Then two-phase flow tests are performed to investigate the flow characteristics, to provide basic data for verifying and modifying the existing models. The results show that, the interfacial drag in beds with coarse particles will result in a decreasing tendency in the pressure drop curves along with the fluid velocity, and the the effect of interfacial drag should be considered in the debris coolability analysis models for beds with coarse particles. Compared with the existing models, the new model shows relatively satisfactory forecasting ability, and the predictions have favorable agreement with existing experimental data under various conditions. This modified model could be applied to calculate the pressure drops of two-phase flow in coarse-particle beds.

Observations of fouling biofilm formation

1981 ◽  
Vol 27 (9) ◽  
pp. 910-917 ◽  
Author(s):  
W. F. McCoy ◽  
J. D. Bryers ◽  
J. Robbins ◽  
J. W. Costerton
Keyword(s):  
Biofilm Formation ◽  
Fluid Velocity ◽  
Frictional Resistance ◽  
Filamentous Bacteria ◽  
Sampling System ◽  
High Fluid ◽  
Recycle Reactor ◽  
Extracellular Materials ◽  
Induction Times ◽  
Biofilm Development

Fouling biofilm development was monitored in a completely mixed tubular recycle reactor. A unique sampling system allowed direct (brightfield, epifluorescence, and scanning electron photomicroscopy) and indirect (increased fluid frictional resistance) observations of biofilms. Low fluid velocity (138.5 cm/s) experiments had shorter induction times and biofilm matrixes which included firmly adherent filamentous bacteria. High fluid velocity (265.4 cm/s) experiments had longer induction times with firmly adherent filamentous bacteria present only after the accumulation of extracellular materials. In both cases the fluid frictional resistance increased after filamentous bacteria became a permanent part of the biofilm.

scholarly journals High Fluid Velocity and Narrow Channels Enhance the Influences of Particle Shape on Colloid Retention in Saturated Groundwater Systems Under Favorable Deposition Conditions

2021 ◽  
Vol 3 ◽  
Author(s):  
Ke Li ◽  
Huilian Ma
Keyword(s):  
Particle Shape ◽  
Rotational Diffusion ◽  
Fluid Velocity ◽  
Pollutant Removal ◽  
Shape Effect ◽  
Particle Rotation ◽  
Flow Channels ◽  
High Fluid ◽  
Groundwater Systems ◽  
Deposition Conditions

Many particulate pollutants in the environment exist in non-spherical shape, but the influences of particle shape on pollutant migration and removal in groundwater systems are not well-understood. In this work, we simulated the three-dimensional translational and rotational motions of rod-shaped colloids in simple flow channels characterizing groundwater flow paths, with an aim to elucidate the underlying mechanisms for rod retention. Through an investigation of the interplay of multiple factors (e.g., aspect ratio, particle size/density, flow shear, channel dimension, and orientation relative to gravity), we determined under what conditions particle shape has the most pronounced impact on transport and retention under favorable deposition conditions (i.e., lacking repulsive energy barriers). Our results showed that in many cases, medium sized rods of ~0.4–2 μm in equivalent volume diameter exhibited much improved retention compared to equal-volume spheres, since for that size range, particle rotation from shape-induced fluid hydrodynamics and rotational diffusion were both important, which caused rods to drift considerably across flow streamlines to intercept collector surfaces. Particle rotation also allowed rods to travel farther downstream along flow channels for retention compared to spheres. The differences in retention between rods and spheres were more evident at relatively high fluid velocity, narrow flow channel, or when flow direction aligned with gravity. Our findings demonstrated that the effect of particle shape on pollutant transport and migration in groundwater systems was essential and provided important guidelines in optimizing parameter designs to utilize particle shape effect for better pollutant removal.

Investigation of Characteristic of Flow Induced Vibration Caused by Turbulence Relating to Acoustically Induced Vibration

2014 ◽  
Author(s):  
Masato Nishiguchi ◽  
Hisao Izuchi ◽  
Gaku Minorikawa
Keyword(s):  
Pressure Drop ◽  
Fluid Velocity ◽  
Low Frequency ◽  
Piping System ◽  
Flow Induced Vibration ◽  
Pipe Wall Thickness ◽  
Large Pressure ◽  
Study Results ◽  
High Fluid ◽  
The Difference

In the flare piping system, it is known that piping vibrations occur caused by Acoustically Induced Vibration (AIV) and Flow Induced Vibration (FIV) corresponding to high flow rate, high pressure drop and relatively thin pipe wall thickness. For FIV, turbulence generated at combining tee with high fluid velocity results in low frequency piping vibration. For AIV, large noise produced through a component with large pressure drop results in high frequency piping vibration. Carucci and Mueller shows the several cases with piping failure due to AIV and most of these cases the piping failure occurred at the combining tee. In these piping failure cases, the velocity at the combining tee would be quite high close or equal to sound speed and this means piping vibrations could occur due to FIV in addition to AIV. This paper shows the investigation results of FIV at combining tee with 90 degrees using experimental data. The results are compared to the previous study results for 45 degrees combining tee and the difference between 90 and 45 degrees tees are discussed in the view points of pressure fluctuation and piping vibration. This paper also shows that the vibration index proposed by authors is quite effective to evaluate the vibration level caused by FIV for both of 90 and 45 degrees tees. This proposed vibration index is applied to failure and no failure cases presented in Carucci and Mueller paper with some assumptions and it is suggested that the vibration indexes for failure case is relatively higher than those of no failure cases. And this suggests that not only AIV but also FIV could affect the piping failure reported in Carucci and Mueller paper.

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